Yealink T53w not provisioning or registering

[ash720]

We have an on premise 3CX setup with a number of Snom and Yealink phones. One of the T53w phones stopped being registered and is not re-registering. Others work fine (but with different users). I haven't tried reprovisioning the working phones.

I know there are many similar topics, but I have gone through them and tried/tested all of the solutions and am still no further.

SSL certificate. We have a 3cx.co.uk domain and I have followed instructions to force a new certificate. Email confirmation of new certificate received this morning. Sslchecker points to correct IP address, but picks up our ssl certificate for our main domain (similar name before 3cx.co.uk). Could this be the issue?

Current firmware, factory reset, IP Phone added via webclient login. Phone then shows up under phones on management console, but no response if I try to assign it to the user.

I have been going round in circles, any help greatly appreciated.

 

[SteveITS]

When it is on the 192.168.1.xxx network what is Outbound Proxy set to? It should be itself.

Does this phone connect on any other external network or is the problem specific to one network?

I keep thinking "factory reset and start over" but you said you did that already.

 

[ash720]

It now works!
Newest version of 3CX installed and a newer firmware version for the phone became available since I started this topic. Maybe those solved the issue.
The only other thing I did differently was follow the advice on another thread of factory reset rather than simply restarting the phone post-installation.