Solution: Temporarily disabling WAN2 after failing back to WAN1 will reset whatever condition(s) cause this. Tested on a USG-PRO-4 but should work on any USG variant with a two-interface failover WAN ...
This repo contains the files you need to succesfully configure the USG with KPN FTTH with IPTV and IPv6 enabled ... interfaces which are needed for internet (vlan 6) and IPTV (vlan 4). IPv4 is ...