Halo: Campaign Evolved - Login Failed

I'm curious if anyone else has been running into this warning on Steam?

Played this morning on my HTPC when the game released, then tried playing on my desktop PC this evening and got this warning. Tried opening it on my HTPC and it gives the same warning, so I couldn't play on either device. I tried to log out and log back in and the only thing that worked was waiting 30+ minutes to open the game again.

My saves don't sync the first time the game is opened, which is what makes this dreadfully cumbersome. I haven't bothered with Microsoft support because they have, in the past 10 years, never resolved an issue for me with online services.

Login Failed - Your account appears to be signed in on another device. Sign out there first, then try again.