AdrianH54 wrote:
That is something to look out for if you factory reset, the router will default to 1500 MTU , PPOE works at 1492 or less.

My modem and router can use an MTU of 1508 , try it and the line is unusable.

Ah yes that might explain it then! - I did a factory reset, then rebuilt the settings from scratch but didn't notice the MTU may have changed itself. I ran the MTU test and it said 1492, so I'll leave at that and see how it goes.