I got a Profile Sync Error on January 8, 2017. I tried everything to work, but nothing happened, so I decided to play Forza Horizon 3 instead. The next day, I thought I don’t have a Profile Sync Error anymore, but I have very slow connection on Halo Waypoint. My Xbox has a way faster connection.
> 2535468263937860;1:
> I got a Profile Sync Error on January 8, 2017. I tried everything to work, but nothing happened, so I decided to play Forza Horizon 3 instead. The next day, I thought I don’t have a Profile Sync Error anymore, but I have very slow connection on Halo Waypoint. My Xbox has a way faster connection.
Weird problem. 
You might find a good answer from Microsoft support itself. This might not be a halo problem.
> 2535468263937860;1:
> I got a Profile Sync Error on January 8, 2017. I tried everything to work, but nothing happened, so I decided to play Forza Horizon 3 instead. The next day, I thought I don’t have a Profile Sync Error anymore, but I have very slow connection on Halo Waypoint. My Xbox has a way faster connection.
When you say “tried everything”, what does that mean specifically?
I had this problem last night as well. Any customization done to my toon would revert back to the default Spartan. Helmet, Armor, Emblem, color…
There were SEVERAL other players that had the default Spartan items too. The my small team of three had all gotten reset for some reason.
Ok, Halo 5 for me is working right now.
Had this issue as well. Same thing: Profile Sync Error, saw a number of generic recruit Spartans in games, no emblems appeared, no customization available. I could still play games but occasionally a popup would hit me mid match with the Profile Sync Error text.
Seems to be working just fine now.