@GeneraalSpeknek, not sure it this would be a problem, but the network your using is not a reserved public network address and also noticed that the DHCP range starts on the interface IP. Can you try...

@Kimberley_j87 that router's is a beauty. 🙄 This all looks correct. The yellow wire goes from ONT #2 (GE1) to Router #6. Blue wire goes to the lounge (I assume) What's the flat white wire? Does that...

@Kimberley_j87 ONT needs to be plugged into the router's WAN port to use more than one device which is what you want.

@GeneraalSpeknek, I do my best to help and improve my networking karma. The device connection B-2 need so be untagged member and native network of 99. (That you did) Then ports along the path to the...

@Kimberley_j87 it would still work for one device if ONT is plugged into LAN port and not WAN.

@GeneraalSpeknek, sorry if I'm missing it, but what's the test switch profile look like. It should have the test (99) vlan as the native vlan and untagged member.