Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.70
Broken: version: 2.81 (sub 5), branch: master, commit date: 2019-09-03 16:04, hash: rBb3b59e3b5657
Short description of error
There's an undocumented nonsensical collections section in the rigid body options (just below the sensitivity settings)
unless this is it from the manual? If so, the description is about as clear as mud :) :
Allows rigid body collisions allocate on different groups (maximum 20)."