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!
That is weird then. I’d change dynamic DNS providers.
I don’t know which other ones they have done this to. Also it’s a faff to move domain now. If I’d move domain, I’d just buy one as the IP is static.