Sangoma Connect/Talk issue on LAN

Sangoma Talk system up and running by years.
Devices have always worked fine from internet as well via wifi connection to pbx same subnet (lan DNS entry for FQDN is static to pbx LAN ip into firewall),
few days ago they failed to run fron inside lan, without apparent reason.
App shows “available” state but with grey-green alternating blink dot.
No changes on firewall rules or pbx neither.
Where can I start troubleshooting ?

Turn off all firewalls temporarily and see if they connect.

Since it’s all phones (I assume) then it’s something systemic on your network. Do you use VLANs? Were any VLAN settings on the network changed recently? Any network router/firewall changes?

If the apps are on PC’s were there any mass PC updates done?

Firewall is not involved in LAN traffic betwen app (smartphone) and pbx.
It is involved in traffic coming from internet, but it works fine.
No VLANs

Firewall is not supposed to be involved… But it can be if something is not working properly. It’s always the first thing I check. Drop the FreePBX firewall momentarily and test.

what is the PBX running on? PC? sangoma hardware?