Yealink, provisioning and Sophos firewall

[UCUC]

Hi,

All of our phones are behind a (sophos) firewall.

All ports are open from phone network to provisioning server. (ANY to URL Provisioning)


This works, but we are seeing some strange drops on our firewall comming from the provisioning URL.

Also when we push "update Configuration" no red led is blinking.


When a phone is installed at my home internet, everything works much faster with updating, red light blinking etc.

What are we missing in our (Sophos) firewall?