#43386 added some checks for illegal implicit casts in IL, after that went in COR_PRF_MONITOR_CODE_TRANSITIONS will trigger an InvalidProgramException.

I haven't debugged fully, but the likely cause is that NDirectStubLinker::EmitProfilerBeginTransitionCallback or NDirectStubLinker::EmitProfilerEndTransitionCallback (or both) have always emitted invalid IL and need to be fixed.