Hey everybody - just chiming in here since I just (seem to have) solved this issue in my particular context after a week of frustration.
I recently bought a second hand Fireface UC and eagerly hooked it up to my 2018 Macbook Pro 15" (6-core i9, 32GB Ram, CPU-throttling-update installed, High Sierra 10.13.6, running Ableton Live 10) along with my Push 2, Midi Fighter Twister and iPad through a high quality USB C - USB A hub, only to find exactly the type of glitches and dropouts described in this thread.
After trying firmware-updating the interface, installing the 3.08 driver, replacing the USB-hub with another one, replacing all USB-cables etc. I still had the issue, and almost decided to sell the interface on. After all I bought it for its famed driver stability...
BUT then I accidentally discovered that whenever my Push 2 weren't connected or on, the problem vanished. I don't know what is going on, but it seems that whenever the UC and the Push 2 is handled by the same USB controller problems occur.
I simply plug the Push 2 into a separate adapter/hub connected to a USB C port on the opposite side of the MacBook and everything is running as it should (for now anyway).
So for anyone still experiencing this problem while using other connected USB-gear - if you haven't already, try isolating the RME stuff to it's own USB port.