Solved:Clock keeps resetting

As you probably know, the 'internal' setting is only appropriate for pure MIDI projects driving direct-monitored external hardware.
 
If there's any audio-based content in the project at all, the clock will default to Audio. This includes the audio metronome, soft synths, and input monitoring an empty audio track.
 
 

Thanks for the suggestions; however, this are no audio tracks, soft synths or any other audio components. The project is pure MIDI.

Well I was unable to get the clock to stick to internal at all. I deleted all buses and unchecked all audio devices. Playback and record timing masters show none or empty. With just one pure midi track, when I press play, the audio engine indicator does not light up, but the project clock source switches to audio. (Manchester)

How strange, my main difference was I started with the 16 midi channel template. It routinely changes clock back to audio. When starting with a blank project adding one midi channel as you (brundlefly) tried, the clock stays internal.
 
Edit: now I see metronome for the midi template is audio. (!)

In response: I always use a MIDI click for the metronome, not an audio one. Also FWIW, the file was created by adding individual tracks, not from any template.
I have disabled the audio interface (Tascam MKII), but am wondering if the problem is caused by the Kronos USB interface that provides both MIDI and audio, even though the Kronos audio is also not being used.
To repeat my original problem: the clock resets itself to audio while working on a project, even though the project has been using the internal clock. It's not a major task to change the clock, but I cannot understand why this is happening.

It happens infrequently while I'm working. Can't locate anything that would trigger it and there's no predictive sign. Just occasionally I'll select the first tempo ratio button and the tempo is not adjusted.