USG60 - Problem with internal LAN.

Good morning,

I have a strange behavior with our USG60 regarding the local LAN port.

Since we changed the network provider every time the provider's router reboots (power loss, random reboot, manual reboot, etc.), the USG changes the internal LAN IP mask. Something that it never had done in the past.

To give you an overview on the USG60 WAN 1 (P1) port is connected to the provider's router (an ADB VM 5722) with the "classic" 192.168.1.1/24 IPs pool.

On P6 is connected to the local LAN with the same IP pool (that's a "heritage" of the past) 192.168.1.1/24. The goal was also to "hide" the actual router by the firewall.

The ports IPs are static.

Pretty easy. Nothing too fancy.

But, as I said, as soon as the router reboots, the LAN1, on the USG60, changes from 192.168.1.1/24 to 192.168.10.1/24 and that forces me to log in, revert the change, and reboot several PCs/components of the LAN because everything is not working anymore.

Before we changed the provider, I had basically no issues. Or, at least, not so "bad" and, honestly, I don't know WHY this is happening and how to fix it.
Except to permanently change the local LAN IP mask and create proper rules in the firewall to forbid the router from reaching it.

I'm using the latest firmware:

Thanks a lot in advance.

Best regards
Giacomo