If you migrate form Skype or another software client to Microsoft Teams Voice, you should disable the call control through your headset device configuration. Through the migration you will use both software client at the same time for different functions like, chat, voice and online meeting.
I use a Jabra Headset, you can use the Jabra Direct to control your headset and disable “Call control with softphone”
If this feature is activated on your headset, calls will be droppt if you leave the call on one of your softphone clients!