We took a look at the attached project and we were able to reproduce the issue.
The problem turned out to be that the skeletons are marked as static (more precisely, Occlusion Static). This tells Unity's occlusion system that these object will not move. But in fact, they do move, so this contract is violated and this is what is causing unexpected results.
We removed all static flags from the skeletons and cleared the occlusion data (see Window > Rendering > Occlusion Culling) and the issue went away. Once you have marked up all skeletons correctly, you may want to rebake occlusion data in Window > Rendering > Occlusion Culling for optimal performance.
So we believe the system is working as designed.
A general advice: You are using the Forward renderer in a scene with many lights. Generally, Forward doesn't handle many lights well, so you may want to switch to Deferred renderer instead. This should improve your overall frame-rate.