you for reaching out to the Community regarding your issue, though I am sorry
to hear that you are experiencing this. Loans do not have the option to relink after being unlinked in Quicken. I'd recommend either readding the account to Quicken or you can instead make it so that your account that pays the loan has the transaction transfer directly into the loan. Generally people prefer the second option as you'll be able to control the principal and interest as well as any extra things.
If you have any questions please let us know and we'll see what we can do.Thanks,Quicken Francisco