I had a very similar issue. I was receiving audio, all looked OK, channel meters reading volume, etc. But during record, was just blank, no ‘recording audio ribbon’ shown, nothing playing back later. I had been doing all sorts of audio part editing. Triple re-checked VST Connections, I have 24 channels coming in. Anyway, I saved the project, shut down Cubase and restarted, reopened project.
When it came back up, it all worked.
I use ASIO4ALL driver, which works mostly, but can get messed up and cause weirdness, pops and clicking noise. Many times it selects what it thinks are default inputs and outputs on its own and on the fly during takes, I have to go turn them back off. Sometimes I have to press the ‘Resample~’ buttonif lots of noise crops up . That usually solves it for awhile. Win10/Cubase 9/MOTU 24Ai/Mackie Big Knob