I've been having this problem since the game launched in November.
I traveled home over the Christmas period and the game worked perfectly there on a Sky connection.
Getting Error Code AFGHIJK N Q S U W Z when I attempt to reconnect after disconnecting.
I believe the problem might be linked to dual frequency routers as I have seen others with the same problem mentioning they also have them.
I've tried connecting to both 2G and 5G with no luck.
Also tried waiting for number in top corner to change before starting the game.
No help from Xbox/Activision/VM so far, hopefully someone can help me out!
Sorry to see you're having trouble with black ops 3. There appear to be many with similar drop outs regardless of ISP. Let's see what we can do to help.
Have you tried a wired connection rather than wireless? Unless the xbox is switching from the 2.4 to the 5Ghz signal (which shouldn't be happening) then dual band shouldn't make a difference.
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I tried yesterday with an ethernet cable and that seems to fix the problem.