Every now and then, TotalMixFX doesn't properly exit after closing its window and can't be killed nor restarted, only solution is to reboot. In fact, it is in a process state of "E" meaning "trying to exit", and no "kill -9" will remove the process.

schwarz            598   0.0  0.0        0      0   ??  ?E   16Jan20   0:00.00 (TotalmixFX)

This is with
Fireface 400 (over a Thunderbolt adapter)
firmware 1.71
TotalMixFX 1.64
Driver 3.38
MacOS 10.11.6
MacBookPro 13" mid 2015