Some objects won't cast a shadow until they're visible (noticeable eg on the left wall when approaching the 1st class gym towards the beginning).
Over-optimized culling?
Might be wrong, but it appears to be screen-space ambient occlusion glitching out. SSAO uses the normals in the output buffers to darken concave sections
Amazing! The gym [1] is particularly fascinating. I wonder how those old rowing machines work.