VoIP calls won't transfer
We had a VoIP system installed last year and it was working before lockdown and home working. Since returning to the office, it still works fine, except it doesn't transfer calls if the transferring phone is in the office. The calls get left in limbo for a while. If we take the handset out of the office, it's fine.
The office has a leased line coming in, through a Cisco ISR 1100 router in to a TZ400. No domain or server, the Sonicwall is also the DCHP &c. So the Sonicwall appears to be the possible problem.