This is interesting. I am a regular Zorin OS Lite user as well and it always remembers the last window frame size and position of the window when it was closed.
There are some few apps that do not support window position/size memory. I do not recall which off hand, but they are all third-party apps.
It may be that you happen to prefer and use some of those apps.
You may need to try devilspie to correct (at least, it works on those apps that lack support). You can read more here: https://wiki.xfce.org/faq#window_manager