Audio processing stops

Three times in the last couple weeks, I have been in the middle of working on a project and Cubase audio processing stops completely. No playback or input audio.

Each time, I checked my interface, but it was up and running normally.

Twice, I was working with larger projects, but this one had one instrument and 2 audio tracks in the project. All 3 times I heard the hard disc spin-up just before it occurred. All my audio is on an SSD as is Windows. Although, I have some of Cubase’s resources (patches and stuff) on a hard disc.
None of the 3 occurrences had anything else in common.

Antone run into this sort of thing?