Secondary ringer recently stopped working on my Mac.

[LynnProspect]

I'm using Teams on an iMac running Big Sur. I use a Plantronics USB headset as my audio device for speaker and microphone, with 'built-in output' set as my secondary ringer. This combination of settings worked fine until a few weeks ago, when the secondary ringer suddenly stopped working. I've tried all the hints and tips I can find online, to no avail.  

[#2]

I have the same issue.

[#3]

Same issue for me, please fix it!

[#4]

We've got the same issue without any solution. This occurs for everyone in the company. Now, headphones cut off every 4 minutes.