I have no idea why but whenever i launch halo 5 during the day it will refuse to work and ive tried everything on my xbox to try and resolve this problem like restarting my xbox and whatnot and all it says is that I have a profile sync error and i cannot connect to the lobby servers. But then suddenly past 9 in UK time it magically starts working. Im a slight bit happy I can play it at all but my friends normally wouldn’t play halo at that time so I just play on my own. I need this problem fixed and I dont know if its my internet or my xbox either. btw the internet I use is sky so yea.
I had sync errors a couple of times when I logged in today. A hard reset resolved the issue.
Test your internet speeds at that time. A lot of providers throttle during peak hours to help with demand.