VoiceEdge app won't work with transferred calls

We have two in-office users that use VoiceEdge instead of their phones.  Both users experience a problem when calls are transferred to them - they can't hear the sending user and the sending user hears a distorted voice on their end, and calls won't transfer.

This only happens when transferring to VoiceEdge, not the other phones.  It affects two users identically.  It started 2 days ago and they have rebooted, etc. trying to solve the problem.