I have a new 2018 model macbook pro i7 quad core and a fireface400. got the two adapters (firewire > thunderbolt 2; thunderbolt 2 > thunderbolt 3). it didn´t work from the start, so I installed the recent rme driver, fireface setting say v 3.35.
I did allow RME in the security section of system preferences and then made a restart.
here the trouble began: macbook pro turned on, the white apple logo & progress bar appeared, very slow progress and at 100% progress bar nothing more happend. tried it serveral times, tried starting with command-r and checking with disk utility first aid, no problems found. restart still didn´t work. called apple support, did hardware test, no problems found. so they told me to reinstall macOS. I did it.. and:

everything works again. RME Fireface400 to my amazement works with the two adapters (no bus power though).
I am now on macOS Mojave 10.14.3

I hope I can happily use my old FF400 for years to come.
 
I still wonder what happened? why the system trouble after installing the RME driver?