How to reproduce:
Install both newest version of MMM and Requiem.
Result:
When game finishes loading, screen flashes several times, and no mob entity dummy renders in menu; only player dummy does. When loading the world no entity/block entity renders either, hand and player entity does not too.
Error:
Appears at the end of the log, after generating assets
[16:34:46] [Thread-501/INFO]: OpenGL debug message, id=1283, source=API, type=ERROR, severity=HIGH, message=GL_STACK_OVERFLOW error generated. Matrix stack overflow.
Fix:
Talked to Pyrofab, lead developer of Requiem, he currently does not know what exactly causes the issue, I do not know either.

Link to issue ticket on Requiem repo:
Ladysnake/Requiem#268