It sounds as though Cubase is losing connection with your audio system and trying to switch to an alternative ASIO. Perhaps losing physical connection might be the cause?
I would suggest a careful check of all cables and connections. Reseat any audio cards, (with power disconnected of course). Swap out cables where possible. At least confirm all connections really solid. If you’re still having a problem then, reload audio system drivers.
Regarding Variaudio, i find that long files slow down graphic response, so take smaller sections of a vocal (say 30 secs) audio bounce in place to make a new version and work with that.
Hope this helps
P