I'm Following along with the Human course. (Blender ver. 4.3.2)
After I made the open mouth and eyes shape key and added details in the multi-res modifier, random spikes around the corners of the eyes and mouth started to appear.
Someone suggested using the Multires Displacement Eraser. That worked at first, but every then and now when I add details to the model and turn the shape key on and off, more of these deformations (spikes) start to appear.
At this point, nothing I know solves this issue.
Any help is deeply appreciated.
Kent goes into trying to solve that common bug in the course. If you keep watching he has to deal with it several times in the course. It's something that has never been fixed and you have to battle it out all the way unfortunately. It's a very hack solution to try and get rid of those and hopefully one day we wont need to go through it all. So donate to the Blender Development Fund I guess.
Just because it didn't happen to me at the same time (plus frequency and severity) as it happened to Ken, I assumed the bug was fixed since he is using an older version. I thought that I was dealing with something else.
Thanks, Omar.