Internet Accounts spontaneously forgets passwords and I can't reauthorize them

I've had this problem before, but I was able to resolve it that time. macOS 10.13.4, everything up to date. Yesterday, Internet Accounts forgot my LinkedIn password and would not reauthenticate. Today, it forgot my Facebook password.

I've tried:

• App specific password.
• Removing the account and re-adding it.
• Turning off 2-factor authentication.
• Deleting associated entries from Keychain.
• Logging out of iCloud, deleting Keychain entries, removing and re-adding the account, then logging back in.

First of all, what the hell—why does this keep happening?! Secondly, what else can I do to fix this short of reinstalling macOS?

I came here looking for answers to exactly the same issue. In my case, both LinkedIn and Facebook started prompting me for passwords on my MacBook, but (oddly enough) not on my iMac.

I've since removed the login keychain items for both, and was able to re-authenticate to Facebook once (which created three login keychain items), only to be prompted again.

No such luck with LinkedIn, though. I get an error message with an un-clickable URL (with a long UUID).

I suspect that either Apple has some sort of subtle date bug or that both services broke their APIs somehow (GDPR might explain the near simultaneity).