Mac pro switch to internal speakers by itself

This happen now and then. I have to go to macs system installation to change Back to dac output.
Sometimes this doesn’t help and have to close and start Mac
Any suggestions why this happens?

Hello @Ulf, do you see this behaviour after you start a song in Audirvana?

no only when i start to listen next day and discover that it plays internal speakers. i say about once a month when i play every day.
never in the middle of a session