Hello Alx,
Welcome to Microsoft Q&A forum.
I understand how inconvenient and annoying it could be when your PC keeps sign you out once in a while. Before we proceed, I'd like to ask a few questions to better understanding this.
- May I know if you remember any changes was made to your computer before this starts?
- Please go to account.microsoft.com/activity to see if there are any activity that you may not recognized.
In the meantime, please try this fix to see if it helps.
- Sign out of your account on all platform and apps.
- Type "Credentials manager" in the search bar and press Enter.
- Remove all entries related to your affected accounts.
- Restart your computer and sign in again one by one to make sure it is okay.
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