Multires behaves erratically on different meshes with similar polycounts. This is a task to gather problematic cases and investigate the issue
- To Do
If it can help, here's one i got recently with a non serious sculpt fortunately with a recent buildbot version, e8c63ca .
It's a variant of the "spike" bug reported several times, variant as it's not a big spike, but similar because it will never go away once it has started happening :
Load the blend and go to Sculpt mode
Make sure (it should be by default after loading) the multires is on level 3 (in total there are 4 multires level on that sculpt)
On the "cheek" you should see this very nasty problem (i didn't sculpt that at all it generated itself while switching between multires levels)
Now use the Smooth brush and smooth it so it's fixed (or more exactly it make you think it's fixed)
Then change the multires level to 4 and .. it's there again :
Go back to multires level 3 and ... it's back (despite we completely smoothed it before)
Now change to multires level 2
And smooth it from there , again it will let you think it's fixed
until you switch back to level 3 , in which ... it's back again
This is exactly the same case as the past reported spikes , this kind of bad bug simpply destroy your sculpt because it can't be fixed once it start to appear as you see from the smoothing attempt, once the bug start happening, it will come back everytime you'll change a multires level.