3 weeks ago we internally migrated the telephony from SfB on Prem to MS Teams. So far, everything went smoothly. Unfortunately, we cannot accept any calls coming in through our switchboards in the Team Fat Client.
It seems to be a local problem with the clients, because the calls can be accepted via the Teams WebApp.
Can you double check if you are still facing the issue? The issue seems to have resolved and multiple customer confirmed the issue is resolved. It was the musiconhold feature which was causing the issue which has been fixed.