Cubase Pro 8 No Audio Playback

I’ve been using Cubase Pro 8.0.35 with no problem until today. The audio tracks are still present in my projects but none of them play back. Also, there is no meter activity in any track during playback. These are simple projects with only a few tracks and no automation. Rebooting Win 10 several times did not fix the problem.

I updated to Cubase Pro 8.0.40 with the hope that it might change the internal Cubase state so that the tracks would play again.
After the update the track did playback for a minute and then stopped playing back with the same symptoms, no meters and no audio.

I’m using Win 10 on a PC and a Focusrite 18i8. Cubase Pro recognizes the Focusrite and the correct driver is loaded.

The problem does not seem to be associated with any unique project settings or drivers. I’d appreciate any help in getting Cubase working.