My normally well-behaved Android (OnePlus 5, Android 8.1, stock current OxygenOS ROM) has started acting weird.
Specifically: some apps (WhatsApp, Google Photos, and maybe this feature or that of other apps) think there's no internet, and the phone can't see Chromecast devices on the LAN. Otherwise, fine. Sometimes, WhatsApp is fine but refuses to run backups. When I'm away from home, it seems to behave OK.
My phone behaves sometimes (ie when at the office), but not at home. We're on 2Degrees with a FritzBox router in (I think) the default config. What can I do to track the problem down? Other devices on the same LAN can see Chromecast and use WhatsApp, so it doesn't feel like an ISP issue.
I'm suspecting it might be some networking support / config (ie can't connect to Photos or WhatsApp servers over $feature, where $feature might be IPv6 for example). But I'm not sure how to trace the problem down from here.
Suggestions (or wild guesses) most welcome :)