Repeated sudden loss of audio output

Cubase 12 pro, Win 10, intel I7, 24 gigs ram, Zoom L12 and UAD Apollo Solo interfaces, (which I shift between). I can be working on a simple project with only a midi track and two audio tracks. I may make a routing change or maybe NOT even making a routing change when all of a sudden playback will stop sounding, (but levels in mixer shows it’s being sent to master bus). Then, after verifying I SHOULD be hearing something, resume playback and NOW NO audio levels showing. Midi continues to play fine. Close project, reopen, no sound or waveforms. Open another which had worked before, NO Sound either. Restart Cubase, NO sound. Restart Apollo, no sound, reboot computer, no sound. Shut down Cubase, computer, Apollo, Zoom livetrack mixer, (cry silently for 2 minutes) and restart everything. Computer, Zoom, then Apollo, load project. Everything works fine!? Any idea what might be causing this? It happens regularly.

Maybe a concurrent software trying to use the ASIO driver in parallel?
In case you not already have given Cubase exclusive control over the audio interface, i suggest to try this.

Do you mean check the "release Driver when application is in background (under studio setup/asio driver?)

No.

I was thinking about the audio interface settings in the studio/studio settings menu. I guess you will have an ASIO driver of your audio interface there. A lot of audio interfaces i know offer a setting to grant cubase exclusive access to the audio interface, meaning it prevents other applications from trying to get access to the audio interface while Cubase is running.
Maybe your problem comes from an application (maybe running in the background) trying to get access to the audio interface and therefore interfering with Cubase. So in case you have a related setting, it might be worth to check if it that changes the behavior.