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!
O2 has an on-by-default security filter that blocks all sorts of “bad stuff”. For me, it was preventing connecting to any PIA VPN servers. Ping their customer support and they can disable it for you.
Telstra here in Australia seems to have this as well. Not sure about duckdns specifically, but last night I found out that they block a few monero mining pools. I emailed them about it, and apparently it’s based off of virustotal ratings. They wouldn’t turn it off, but they told me it’s “trivial to bypass” (their words), suggesting google or CloudFlares DNS, or a VPN
those “security filters” are the worst, a few years ago vodafone with their “rete sicura” was blocking githubcontent and it was a nightmare to have them disable the service for me, the operator was like “but this is a free premium service that protects you”
I’ve emailed them. See what they come back with. I mean unless they block SSH, Wireguard and Tor, I’ve got to hand work arounds. I just doesn’t like them fighting me.
If they take long or don’t resolve it, try the live support chat. I used the chat inside their app to request it and it was unlocked pretty much instantly.
I tried their help chat bot and it just said to install their app after a few exchanges. My phone is de-googled, so good chance their app won’t work. Plus, I avoid installing closed apps as it is unhygienic. Each one seams to demand access to contacts and location and won’t work if you deny it. Dystopian present, let alone future.