Hi,
I was wrong. This seems to be on the driver side, now.
I can reproduce the bug even with macOS 10.13 when UR28M or UR824 (i.e. Yamaha/Steinberg Audio Devices without MIDI) drivers are installed in the system. I couldn’t reproduce it in the past and now I can reproduce it on both (10.13 and 10.14).
Could you try to install an older Yamaha/Steinberg driver for your UR28M or UR824, please?