Sorry for leeaving you hanging, Galaxy… I have been wiping and reinstalling Zorin 15. 
Setting up zsh with p10k, now…
And installing my preferred D.E.
To downgrade GDM3;
Use your normal terminal install command, plus the package version.
First, find your gdm3 version with
gdm3 --version
Then you can look up the package version history and choose a previous version.
The current package in the Ubuntu Repository is 3.28.3-0
This is a short snippet from /var/log/syslog from a Login Glitch.
Jan 30 13:20:26 acer gnome-shell[1435]: clutter_container_add_actor: assertion 'CLUTTER_IS_CONTAINER (container)' failed
Jan 30 13:20:26 acer gnome-shell[1435]: JS ERROR: GLib.Error g-unix-error-quark: Too many open files
Jan 30 13:20:26 acer gnome-shell[1435]: Object St.BoxLayout (0x562060b1c660), has been already deallocated — impossible to access it. This might be caused by the object having been destroyed from C code using something such as destroy(), dispose(), or remove() vfuncs.
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: == Stack trace for context 0x56205ba1b290 ==
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #0 7ffe91e87020 b resource:///org/gnome/shell/ui/popupMenu.js:727 (7ff844527c10 @ 22)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #1 7ffe91e870e0 b resource:///org/gnome/gjs/modules/_legacy.js:82 (7ff8447b0b80 @ 71)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #2 7ffe91e87190 b resource:///org/gnome/shell/ui/popupMenu.js:745 (7ff844527ee0 @ 23)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #3 7ffe91e87250 b resource:///org/gnome/gjs/modules/_legacy.js:82 (7ff8447b0b80 @ 71)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #4 7ffe91e872f0 b /usr/share/gnome-shell/extensions/zorin-printers@zorinos.com/extension.js:106 (7ff8040b4280 @ 232)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #5 7ffe91e873b0 b resource:///org/gnome/gjs/modules/_legacy.js:82 (7ff8447b0b80 @ 71)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #6 7ffe91e87450 b /usr/share/gnome-shell/extensions/zorin-printers@zorinos.com/extension.js:203 (7ff8040b4670 @ 28)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #7 7ffe91e87510 b resource:///org/gnome/gjs/modules/_legacy.js:82 (7ff8447b0b80 @ 71)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #8 7ffe91e87550 I self-hosted:975 (7ff8447f0280 @ 392)
Jan 30 13:20:26 acer gnome-shell[1435]: clutter_container_get_children: assertion 'CLUTTER_IS_CONTAINER (container)' failed
Jan 30 13:20:26 acer gnome-shell[1435]: Object St.BoxLayout (0x562060b1c660), has been already deallocated — impossible to access it. This might be caused by the object having been destroyed from C code using something such as destroy(), dispose(), or remove() vfuncs.
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: == Stack trace for context 0x56205ba1b290 ==
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #0 7ffe91e87040 I resource:///org/gnome/shell/ui/environment.js:41 (7ff844785430 @ 20)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #1 7ffe91e87130 b resource:///org/gnome/shell/ui/popupMenu.js:652 (7ff844527700 @ 61)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #2 7ffe91e87240 b resource:///org/gnome/gjs/modules/_legacy.js:82 (7ff8447b0b80 @ 71)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #3 7ffe91e872f0 b /usr/share/gnome-shell/extensions/zorin-printers@zorinos.com/extension.js:109 (7ff8040b4280 @ 345)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #4 7ffe91e873b0 b resource:///org/gnome/gjs/modules/_legacy.js:82 (7ff8447b0b80 @ 71)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #5 7ffe91e87450 b /usr/share/gnome-shell/extensions/zorin-printers@zorinos.com/extension.js:203 (7ff8040b4670 @ 28)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #6 7ffe91e87510 b resource:///org/gnome/gjs/modules/_legacy.js:82 (7ff8447b0b80 @ 71)
Jan 30 13:20:26 acer org.gnome.Shell.desktop[1435]: #7 7ffe91e87550 I self-hosted:975 (7ff8447f0280 @ 392)
the above section is just repeated many times
and then finally at the end our type [ 1 ] error
Jan 30 13:20:26 acer gnome-shell[1435]: clutter_container_add_actor: assertion 'CLUTTER_IS_CONTAINER (container)' failed
Jan 30 13:20:26 acer gnome-shell[1435]: JS ERROR: GLib.Error g-unix-error-quark: Too many open files
Jan 30 13:20:26 acer dbus-daemon[707]: [system] Successfully activated service 'org.freedesktop.GeoClue2'
Jan 30 13:20:26 acer systemd[1]: Started Location Lookup Service.
Jan 30 13:20:26 acer gnome-software[2111]: no app for changed alternate-tab@gnome-shell-extensions.gcampax.github.com
Jan 30 13:20:26 acer gnome-software[2111]: no app for changed apps-menu@gnome-shell-extensions.gcampax.github.com
Jan 30 13:20:26 acer gnome-software[2111]: no app for changed auto-move-windows@gnome-shell-extensions.gcampax.github.com
Jan 30 13:20:26 acer gnome-shell[1435]: Creating pipes for GWakeup: Too many open files
Hope this helps in diagnosing my system problem. Thanks for your patience. 
have you checked for a memory leak?
I tried to install a previous gdm3 version but I get this error message
The following packages have unmet dependencies:
> gdm3 : Depends: libgdm1 (= 3.28.0-0ubuntu1) but 3.28.3-0ubuntu18.04.6+zorin1 is to be installed
> Depends: gir1.2-gdm-1.0 (= 3.28.0-0ubuntu1) but 3.28.3-0ubuntu18.04.6+zorin1 is to be installedI don’t know how to do that for system processes. Please tell me.
Try:
sudo apt install - y libgdm1=3.28.0-0ubuntu1
sudo apt install -y gir1.2-gdm-1.0=3.28.0-0ubuntu1
sudo apt install -y gdm3
Alternatively, you can try:
sudo apt --fix-broken install
It’s that time of morning- I have to drive to the airport- back in about an hour or so.
In the link I posted above, please scroll down far enough to see
“Steps to find memory leak”
It has detailed step by step walkthrough that may help.
Once you go through the steps you can post the memory dump here in this thread.
Downgrading gdm3 didn’t help. The problem still exists.
I tried to follow the memory dump step by step but on running strings command on my memory.dump file didn’t gave anything as output. Besides I think I didn’t much understood diff command step and what do actually I have to look for in the difference.
I ran all this on a process call gdm with command /usr/bin/gnome-shell , I am not sure even if I did that correctly.
Do the output from syslog that I gave really not help in identifying the problem ?
Well, it was worth a shot to roll back GDM3. You can roll it back forward, if you like.
sudo apt full-upgrade
The only output I see in the logs above that I think relate is the one I quoted that made me immediately think that too many file descriptors are open. You also mentioned
JS ERROR: GLib.Error g-unix-error-quark: Too many open files
Normally, cleaning out some space can resolve the issue. In your case, though, it is affecting Login and On Wake. Which means cache and such should have cleared on logout.
On the steps in the link- It may be outdated.
Can you run in terminal:
gnome-shell --version
and post the output here.
Same with:
cat /proc/meminfo
You might consider using htop to display memory usage, then run htop in terminal and let it run while you work on other tasks and go about your normal computering business- IF you notice a slow down or performance drop, look at the terminal window running htop for a large wad of memory being gobbled up.
sudo apt install htop
htop
and you can relay that output here.
Here is an example of htop running on my machine:
GNOME Shell 3.30.2
MemTotal: 7995024 kB
MemFree: 3701968 kB
MemAvailable: 5164916 kB
Buffers: 544964 kB
Cached: 1577884 kB
SwapCached: 0 kB
Active: 2483744 kB
Inactive: 475604 kB
Active(anon): 1557880 kB
Inactive(anon): 19084 kB
Active(file): 925864 kB
Inactive(file): 456520 kB
Unevictable: 719512 kB
Mlocked: 16 kB
SwapTotal: 9999356 kB
SwapFree: 9999356 kB
Dirty: 276 kB
Writeback: 0 kB
AnonPages: 1556144 kB
Mapped: 560256 kB
Shmem: 740468 kB
KReclaimable: 389308 kB
Slab: 458648 kB
SReclaimable: 389308 kB
SUnreclaim: 69340 kB
KernelStack: 15424 kB
PageTables: 57188 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 13996868 kB
Committed_AS: 7458228 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 31764 kB
VmallocChunk: 0 kB
Percpu: 2624 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 kB
ShmemHugePages: 0 kB
ShmemPmdMapped: 0 kB
FileHugePages: 0 kB
FilePmdMapped: 0 kB
CmaTotal: 0 kB
CmaFree: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 0 kB
DirectMap4k: 212604 kB
DirectMap2M: 5922816 kB
DirectMap1G: 2097152 kBAlmost 14 gigs in your commit limit. You are not even using any swap space currently.
Are you working with heavy resource or graphics intensive projects during the times when you have the login issue and errors? Can you recall any software you were consistently using each time (Not including Gnome-shell :P)
Firefox is the most resource intensive app that I use. But as I said before, This problem occurs even if I have empty workspace.
Ok. I was hoping that you might say it was GImp or some non-integrated software that we could narrow doing a possible memory leak to.
what does (terminal) this yield:
ulimit -n
?
1024
.
Ok, can you increase your limit:
sudo nano /etc/systemd/system.conf
arrow key down to the line that says:
#DefaultLimitNOFILE=
Remove the hashtag in front of that line…
and change it to
DefaultLimitNOFILE=65536
Save and exit
ctrl+x
hit y key to say yes to save
hit enter key to save as current file
Terminal will revert to normal.
EDIT: Correction, it is in one more file, too:
sudo nano /etc/systemd/user.conf
And repeat all the same steps above.
At this point… can only test and see what that results in with use.
I made a text file using grep on PID
and hence got a cleaned version of everything that was happening in that GNOME shell process at an ongoing Login Glitch.
Then I did a search for (in the text file)
and that number came out to be 256
Which is a number that easily catches attention of a person good with binaries.
I searched for this error on web
and found that it was generated due to some extensions on GNOME on ubuntu 18.04, which is what Zorin 15 is based on. Here is one such link
This appears to be an extensions related problem even in my case.
I would find out more. Please keep assisting me.
I wonder if I should have you helping me.
I did see some errors related to extensions in your logs- including gcampax. But I was more dismissive of those.
You might check your version of JDK.
If you like, you can try removing and reinstalling the extensions.
sudo apt remove --purge gnome-shell-extensions-zorin-desktop
After Removing, reinstall:
sudo apt-get install gnome-shell-extensions-zorin-desktop
The below list is based off the gcampax-
sudo apt-get install gnome-shell-extension-zorin-printers
sudo apt-get install gnome-shell-extension-printers
sudo apt-get install gnome-shell-extension-zorin-app-grid
sudo apt-get install gnome-shell-extension-zorin-window-move-effect
Before reading this i did a --reinstall command on that package, but that didn’t help. I will try now purging it. But first I am preparing a ZorinOS Lite 15.3 bootable drive (just in case).
I have a timeshift backup. But I am not sure if that backup excludes this error.
I feel your pain. I just wiped and reinstalled Zorin OS earlier today. Fortunately, all my back ups were solid and I am pretty much right back to where I was. Minus gtk 3.24, now.
Interestingly, the reason I reinstalled was due to a Memory Leak in the File Manager that I just could not correct. I must point out, I use Cinnamon D.E. with Nemo FM. Not Gnome.
^That right there, is why I do not Timeshift.
I back up Home Folder and configuration only.
If you don’t want Zorin’s preconfigured GNOME (or xfce), why use Zorinos?
There is more to Zorin OS than just the D.E.
Cpu usage and performance, better backports, less fluff, more stability.
Running Cinnamon on Zorin OS is smooth and fast. Run Cinnamon on Mint and it bogs down after 30mins to an hour.
Sometime back, I did try to get away from using Zorin OS. I did a lot of distro hopping, testing on an aging machine. Zorin OS outperformed all the rest.
There’s a thread about it on the old ZorinGroupForum.