I keep getting this CONSTANT network error message. “Network error: the game connection has been lost: our client has been disconnected from the server.” this has been an ongoing thing from the moment I bought the game. I can’t understand why. I’ve tried changing all settings on my xbox even though I don’t have any issues with other games. I’ve updated all firmware on all devices. I’ve even set up 5ghz connection and I STILL keep getting this error message. I can’t be the only one. I’ve seen TONS of people complaining about this on reddit for months and it just isn’t resolved. It’s not just for xbox, it’s happening for PS5 and PC’s as well. What are we doing here, blizzard? I’ve tried contacting customer service but I haven’t gotten an answer yet. Did anyone else have the same issue and has been resolved? Please share…because I’m very close to snapping this disc in half. 
I’ve been experiencing this as well (Xbox Series X). I get a disconnect every 1-2 hours of playtime typically. This is with fiber internet and a high-performance ASUS router. I’ve set up port forwarding, updated firmware, re-installed the game, reset router, flushed DNS. Nothing really seems to improve the situation.
I’ve been disconnected so many times right at the end of a dungeon. It’s maddening.
I am attempting to play D4 on a slow Sunday morning … suddenly I am being booted off every 2-3 minutes saying network error. I am seeing where people who are experiencing are trying everything imaginable… the thing is I am not dropping service on any other game … just Diablo 4. The game has been a major disappointment to me and I have been a fan for 30 years. It is really insult to injury for fans who are trying to give this game a chance … I really do want to like this game. But this may be the end of the line for our relationship blizzard.
Exact same issue here… several minutes of game play and disconnected. No issue with any other Xbox game.