I’ve just experienced this with my UR28M and the most up to date version of cubase 9.5.21. I upgraded straight from 8.5. It has happened twice. The first time I was able to get the audio hardware option in the Devices menu back again by removing and reinstalling completely the Yamaha tools and drivers. Let me also mention that the hardware rack also dissapears from the rack panel visibility menu making it impossible to use the dsp mixer and FX for monitoring…
The second time, I tried to do the same, and even though the Audio Hardware option now appears on the device/studio menu, and the audio hardware window appears with all its common options when selected, still having issues with showing the hardware rack correctly on the mixer. I can still select the hardware rack to appear on the rack panels, but when I click that actual rack panel on the mixer, its like it is stuck and wont display the usual routing diagram. What I mean is that the panel won’t scroll down to allow me to see the usual diagram configuration… Just found this thread, the fact that it goes all the way to 2016 is a little bit discouraging. This software and hardware should really work seamesly…