Hello George Clarke,
Welcome to Microsoft Q&A forum. It's my pleasure to help you today.
I understand that you are currently unable to sign in to a game, even though you can are log in to the Xbox app. I see that the AI assistant has suggest a few answers, can you please check to see if they work for you?
If that doesn't, I'd like to ask a few questions to better understand the situation.
- Can I have a photo of the screen when you try to log in? Please remember to remove all personal information before posting.
- May I know if you are able to log in to account.xbox.com normally?
- You said that you have reset the Xbox app , but may I know if you have tried to restart the game yet?
I'm waiting for your reply.