im working on a realistic human head i dont know why this is such a common problem for me when the mesh creates random spikes in the case they come out of both ears. i checked in edit mode and the geometry seems to be fine with no loose vertices or whatever. i know this is something to do with the multi res mod but when i do a search i find useless answers that dont help
I believe it's a problem on normals. Visualizing the Normals at the [Properties Region] -> [Mesh Displays] revealed some peculiar normals.
At the same time, recalculation didn't work properly showing that you have topologically wrong faces. (Actually I found some but it's too tedious to name them. Add comment if you cannot find any)
Hope it helps.
I know the issue was posted two years back but I found that if you don't apply the base of the modifier before altering the mesh in edit mode, then you will run into abnormalities like that. Apply the base while in sculpt mode BEFORE switching to edit mode to edit any geometry. If not, when you switch back to sculpt mode you may encounter irregularities like displaced vertices and stretching of the mesh etc.