Phones keep disconnecting since framework 13.0.20

Hi,

Probably since the 13.0.20 framework update, phones in the same network as the server are randomly reported as "not registered".

Totally stable before.
Now the PBX is updated to the latest available version (13.0.22) but still the same issue.
To reduce the impact, I reduce the registry expiration time on the phone to 60 sec.

Any help is welcome.
Thanks.