I have an issue where Teams voice calls will disconnect if another softphone application rings in. For example; i will be on a Teams voice call. My other app (called Worktime) is a softphone. When the softphone is called I get a notification to either Decline or Accept. If I click on Decline, both the softphone AND the Teams call ends. However, if I'm on the softphone first and someone calls me on Teams, both seem to work simultaneously. Windows is updated and so are the hardware drivers. The default audio and microphone devices are the same in Windows and both applications.
This is going to be something very difficult to troubleshoot I would say unfortunately. Not something Microsoft are likely to support and it boils down to two conflicting pieces of software competing. If anything, it sounds like Worktime is the culprit as it interrupts Teams, but Teams does not do the same. Not helpful at all I realise but I think this is going to be one of those "it is what it is" scenarios.