This is a problem that occurs somewhat frequently on my laptop but not on my workstation.
Basically what happens is after a while, zBrush Undo history resets without giving heads up to only 2 items, while the limit is normally set to 400. I am not able to recreate this issue as much as I like however so I can’t point to the exact cause.
I could not pinpoint the reason behind it. But I have eliminated the reasons why it couldn’t be:
Max Undo history under “Preferences” is not affected by this
Storage Space is not an issue.
RAM/Memory is not the issue.
Undo history is never loaded from the ZPRs nor are they saved into the project, as they take more space, I just load all my projects fresh as preference.
This happens on every subtool in the project, restarting zBrush doesn’t fix this issue, you have to do a systemwide reset for it to happen.
My only assumption remaining is that maybe ZBrush gets corrupted when the laptop goes to sleep and that’s why a whole systemwide restart is necessary to get the Undo History to work properly?