Game Center not working
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Game Center seems to be not working after iOS updated to 15.4. When attempting to log into Game Center an error stating “unable to connect to server for reasons unknown” appears and you can click on “cancel or okay” but nothing happens.

anyone else having this issues?

same issue i got. just sorted now. I’m using the game clash of clans. I open the game and it asked for my appleid(since i’m not log in on the game center). input my game center id and pw. now go to settings-game center it automatically logs in the appleid and pw the one you used on the clash of clan games. now log in log out and it works..hope it will solve your issue as well..

Just finished talking with the customer service and they actually proposed a workable solution:

go to Settings > [your name] > iCloud, disable Game Cente, then reable it.

I noticed the issue when I try to join/start a Qwirkle game on my iPhone, I access the game center find my friends but I'm not able to invite them to start a game, the exact same thing is happening with my friend all this happened since I updated my iPhone to 15.4. With my old iPad with an older system, I'm able to initiate games without a problem I can send an invitation to an iPhone with the 15.4 system and initiate a game. I tried all the usual procedures to debug the problem (restart the iPhone, reinstall the Qwirkle app, log out/login game center...) to no avail. Does anyone know what is going on?