If an incoming phone call to a Teams user is forwarded by no response to a reception queue, and the receptionist answers and subsequently attempts to forward to an internal Teams user, the switching will fail.

The error can currently be bypassed by switching these types of calls conferred (hot).

Status 

The error has been reported to Competella who has accepted that there is an error, they are currently working on identifying the root cause so that the error can be corrected.