Can't run Music on my iMac for more than about 15 minutes

I run Music (1.0.6.10) on my iMac (2017; 8MB) running Catalina 10.15.6. Lots of ripped music resides on the iMac's 1.3TB Fusion Drive. I connect the iMac to my receiver/amplifier via cable, using the iMac's headphone jack. This works fine (when it runs I have no issue with sound quality) but after about 15 minutes the iMac displays a message like "are you sure you want to close all apps and log user out? Of course I don't want to but by then Music has stopped. Are there settings that I can change somewhere to keep this from happening; keep the app(s) running and keep the user logged in? I might want to play a big playlist that might run all day.

Thanks

Jeff K.