Hello Martin C Littleton,
As far as I know, call forwarding is one feature of Phone System, and Phone system is also supported by Common Area Phone license, we need to make sure the license is still active. The device you’re using seems to be a Teams certified device and in Teams admin center it shows in healthy status. Since issue occurs after upgraded the device, issue could be related with this recent updating. Is there any way you can reboot this device for checking? I noticed that you’ve already reached our related team for this issue, may I confirm with you if they’re our team from Microsoft 365 admin portal? The policy you’ve tried to re-add is call forwarding police?
Best Regards,
Anna