Fast collision boxes (4x4x4 resolution) are never upgraded to detailed resolution (8x8x8). Possibly related to high CPU load and the fact that collision box thread is low priority.

Should be fixed in
grondag/Exotic-Matter@293969c

Nope, not fixed. Problem is in the algorithm for identifying all the possible disjoint sets of maximal bounding volumes. Some meshes can take several seconds to optimize and with 100's of meshes on the screen it matters. Will revisit thread priority when the math problem is solved.

Fixed in Exotic Matter: grondag/Exotic-Matter#4