This sounds 'possibly' like a profile corruption. This is not too different to a Windows profile corruption except in Cubase you won't lose the facility to access the files you have already created in your possibly corrupted profile.
I say possibly because it's the best test. Cubase tends to save *.bak files so even if a project is not working it should have a backup wherever you saved a file you are having issues with in the same directory.

I would make a backup of your settings then completely uninstall it then reinstall after a reboot. The official backup settings locations here:
- https://steinberg.help/cubase_pro_a...tomizing/where_are_the_settings_stored_c.html


P.S - If you use a lot of plugins raise your buffer size in your audio interface once you get it working too. Cubase works better and you won't get CPU overloads and better sound quality too. if you use a lot of plugins while Cubase will handle it, people blame Cubase but it's actually the audio buffer in Windows and MAC O/S. Lower it for MIDI recording - easy to change as needed.