I just wonder what can cause this. After a bit more testing, it absolutely feels like the 4x 1gbit standard WAN ports are sharing 1gbit of total bandwidth across all interfaces. While traffic coming via the SFP+ 10gbit port and the 1gbit LAN ports are able to push clearly more than 1gbit.

Usually I would not care too much but I am considering upgrading our fibre line to 2 or even 8gbit, but if I can't utilise it on router side, no point, so this needs solving first.

Just a quick update.

Before downgrading the firmware, I decided to invest in a 10gbit sfp+ to rj45 transceiver and connected the ONT to the WAN1 SFP+ port.

This solved my problem and I am now getting clearly more than 1gbit from WAN. Not sure if the fw update borked the load balancing or routing or it introduced a 1gbit limit on all WANs connected via the 1gbit ports. I’m a happy chappy now and shall put this to bed without anymore tinkering.