Hello,
This seems to be a widespread issue. It seems that it affects those that have Facebook setup in System Preferences... > Internet Accounts, and not those that don't and only login via a browser. I haven't had the issue, as I don't have Facebook setup in Internet Accounts.
People are discussing that it may be due to changes by Facebook for the General Data Protection Regulation (GDPR), although this issue has occurred previously. I don't think it is an Apple issue...rather changes made by Facebook.
I suggest that you try removing your Facebook account from Internet Accounts temporarily, and see if that prevents the constant prompting for your login information.
Let us know if that works for you.
C