DHCP config override affects Gateway installation.
If you check Configuration Override on the interface in the DHCP Client Configuration section, then open Status => Interfaces you can't see Gateway IPv4 on this interface, the gateway IP will be not in the routing table, and the Automatic NAT rules will never create.
It doesn't matter if you have a file with for example DHCP option 60, or you leave this field empty.
How to recreate.
1) Open interface configuration (Interfaces=><Yor interface)
2) Check Configuration Override
3) Save and apply
4) Check the Status=>Interfaces