I've been working on this sculpt for over two hours now and all I am doing right now is I have disabled DynTopo to move the mouth a bit more inwards. It works like a charm. After that I hit ctrl+S to save. Then it suddenly reverts to the state before I have moved the mouth inwards and when I hit ctrl+Z that abomination happens you see in the second screenshot. A bit help in that would be highly appreciated, I would hate to loose the work. If I Ctrl-Z further the artifacts just keep getting worse.
Go to edit > preferences.
on interface tab find and enable "developer extras"
your undoes will become slower but more accurate. consider sending a bug report. Here is how: https://wiki.blender.org/wiki/Process/Bug_Reports