Thanks again for everyone's input. The CDN sounds like a likely candidate and I would be inclined to suspect that. However, less than 48 hours after I set up all my static IP's on my SH2 it decided to forget all of them (and it was a ruddy pain to do in the first place) so it's in modem mode doing as little damage as possible. Since I've gone back to my trusty TP-Link (once again running OpenWRT now that I don't need multicast) I've had no problems with 4k on Netflix - it jumps straight in at 4k just like it used to on FTTC. Might be a coincidence, might not.
Nice to be back on this forum anyway
