Raven MTI2- MIDI-and Firewire Oh My!

I think there's nothing scarier than searching the internet for a problem to find that YOU'RE THE ONLY ONE!

PROBLEM- Sending MIDI from external keyboard to computer via RME Fireface 800 results in a midi dropout every 5.5 seconds. (both in Logic and Protools)
I am not aware that I have some esoteric setup.

CAST OF CHARACTERS:
RAVEN MTI2
Imac 2017 27" (two Thunderbolt/USBC3 ports)
RME FIREFACE 800. (Firewire 800)

CONNECTIONS
RAVEN MONITOR HDMI out > Kensington CV4000H (HDMI to USBC adaptor)>Computer (thunderbolt3 port)
RME FIREFACE 800 > APPLE Firewire to Thunderbolt2> APPLE thunderbolt2 to Thunderbolt3 adaptor> Computer (thunderbolt3 port)

Audio is fine going in and out through the myriad of adaptors from the FF800.  
MIDI is fine going from the computer to an external keyboard via the FF800.
RAVEN seems to work fine. 
BUT - Going from the External Keyboard to the computer via the FF800 produces a dropout every 5.5 seconds. 

Unplugging the RAVEN HDMI cable from the Thunderbolt3 port solves the problem!
Connecting everything to an older computer (iMac 2012 with Firewire 800 ports and mini display ports) also works fine.

So how do I connect the Raven to this new computer so that it doesn't interfere with my MIDI?
And.... has anyone had this problem?

Thanks,