First, a quick link as both of these threads are directly related:
It is a fine line to balance; between those that do not want to hear anything other than a solution - and those who prefer to hear an honest answer.
I am going to shoot for an honest answer:
This is a long standing and known XFCE bug.
There are a great many 'fixes'. Some work for some users but not for others.
I have been stricken by this bug, too, in past days and often, an update causes the bug to just go away... Sometimes, an update causes it to reappear.
In recent days, I have cycled through all of the known 'fixes' to no avail.
As I am not using XFCE on Zorin Lite, but have switched to using Cinnamon, I am not currently affected- but I would be if I logged into Lite or XFCE desktop.
The cause is clearly not really known. It appears to be a conflict between Xwindow, Power Manager and Xscreensaver. Most often, changing the settings of the screensaver or even removing it entirely resolves the issue, though you lose the screensaver in the process (some install an alternate screensaver app). But on rarer occasions, that strangely does not always resolve it.
Zabadabadoo had posted a bit of genius on this forum a while back: A separate app that prevents the screensaver from engaging by tricking the computer into thinking the mouse is moved every few moments. The app is called Caffeine. I am told it is available in the Software Store.
This does not solve the problem in any way. It just prevents the screen from automatically locking and therefor the problem affecting the user.
And, like all 'fixes' for this bug, it comes with the caveat that a user can no longer rely on the computer to auto-lock if they walk away from the machine. But it does prevent the problem from arising that results in needing a hard reboot to overcome.