Sort of an update, I think the problem manifested again tonight. I was kinda drunk and can't really say what I did, but I'll just try to give an account of tonight's happenings and leave the conclusions open for someone else.
So I wanted to play some SC5 after having played some GoW3. I was signed in on a wireless controller and just started SC5 from the arcade stick, signing in to my normal profile when the game noticed the arcade stick had no attached profile. At this point I started to suspect problems since in the astral home I saw my rivals having the default SC5 player cards insted of the ones they usually have. Since I intended to play SC5 with one of my friends I proceeded to try to create a player room, and I then noticed I couldn't set a title for the room. I don't recall exactly what it said, but it was something like the current profile doesn't allow setting a title. At this point I didn't proceed with creating the room, but I suspect that had I done so no one in the room would have been able to see my CaS and I wouldn't have been able to see theirs. What I did instead was too open the XBOX home menu and fool around, this is a bit hazy but I think the only thing I did was change voice playback from being only headset to being both headset and speakers (after taking a cue from Wandrian). I also checked the options in SC5, but I think the only thing I managed to change there was my player card. What I did then was sign out from the home menu, the game detected that and kicked me to title screen, I started and signed in again and then I could see my rival's player cards. I then created a room and all CaS worked.
This is all a bit vague I realize, but hopefully someone could make some sense of it.