It too me a while to work out why my Nextcloud stuff wasn’t working on my phone. It wasn’t until I went to http://duckdns.org on mobile data I saw the block. I had changed ISP from one with IPv6, which I had setup, to an ISP without it, and thought it might be that. But it was just coincidence.
I’ve written to O2 but I doubt they will change anything, so I’ll be changing network.
So heads up UK O2 self hosting people!
Interesting.
I have no idea how the piggyback operators work (ie, purely financial, nothing technical?), but a quick check shows Tesco (uses O2) responds the same way.
I’m lucky to have static IPs, but I have a noip.com and that appears to work ok, so it can’t be a blanket policy on dynamic DNS per se.
Giffgaff uses o2 and also blocks duckdns. Additionally, whatever blocklist my employer is using also blocks it, so it’s probably a common thing now.