Have you tried swapping your cat5 / cat6 cables for the hardware? Intermittent connection could be your issue.
If you'd seen my earlier posts you'd know I've tried it at different houses, with different routers and modems, on different ISPs, and with both wired and wireless connections. Every time I lug it to someone else's house during a period where it's an issue, or connect it to my phone's wireless access point, a visiting friend on another network's phone's access point, or whatever, it doesn't matter, the problem persists. And as soon as the ability to load in comes back on one connection, it comes back on all of them. Same issue for my friends any time it happens to them.
It definitely seems account-based though, because it doesn't hit everyone all at once, but when it does hit one of us, it's consistently around 8-12 hours or so, and affects us wherever we try to log in from.
Alas, I've not been able to confirm my hypothesis about it being an issue with logouts, since I seem unable to replicate it by hard restarting my xbox while the game is running. So that idea seems a bust. The game's loaded fine all day today for me.
Sadly testing it on multiple xboxes is not an option just yet since all my xbox friends live in other cities, so unlike my friends in my neighbourhood who let me use their internet connections for previous tests, I can't really just pop round to their house while it's happening and see if I can log in on their box
(and I'm not going to leave my account set to autologin on someone else's console, and wouldn't expect them to trust me with that either to see if I could log their account in on mine) so I'm gonna have to wait on that test to see if logging in on a box with none of my save data present and telling it not to download my cloud saves fixes the issue the same way that deleting save data has worked as a temporary fix for some people.
edit ooh, at midnight exactly it started up again. with a crash exactly at midnight, followed by constant connection errors.
edit the second: eventually after many attempts, it logged me in. repositioned me elsewhere in the system, but this time decided I no longer have horizons. That's a new one. I didn't realise it was even
possible to log in in the non-horizons client on the XBox if you own Horizons. That was why the fix for getting stuck planetside only ever worked on PC and needed Frontier's intervention via a support ticket to fix on console.