Payment detail missing - Loan Account

That looks to me as if your loan account is activated for online information downloading.

Just my 2cents' worth …
I would not bother attempting to activate any loan or mortgage accounts for downloading. I would just simply set them up as "offline" (manual) loan accounts with a Scheduled Reminder to record the monthly payment from your checking account.
(Not discussing LOC or HELOC accounts here. They should be set up as credit card accounts)

At least in Quicken for Windows, an online-connected loan or mortgage account does NOT have a transaction register. All data shown in the account come from whatever information the bank downloads to you ... if this process works at all.

As a result of being connected, the scheduled payment transaction reminder cannot transfer the amount of principal paid into the (non existent) account register and must use a category, usually something like Loan:Principal, instead. The category seems to vary with the Loan Type you selected when creating the loan account in Quicken.

Effective with Quicken Windows 2018+
you can deactivate an online-connected loan account and regain full control over your transaction register. However, you should still review the Scheduled Reminder (or Memorized Payee List entry) associated with the monthly loan payments to ensure they now transfer Principal to the loan account register and not to a Category.

If you're a Q Mac user, you should be able to do something similar about setting up and maintaining an offline mortgage account together with a correctly calculated Scheduled Transaction Reminder for the monthly payments from your checking account.

You're welcome.
Do be sure to verify that the monthly payment transactions are set up correctly as a Scheduled Reminder and that the Splits do correctly transfer Principal to the mortgage account register, the Interest category and optionally the Escrow account using a similar format to this example:

Record this reminder before the payment due date, before the payment confirmation arrives in a download from the checking account.

To me that looks like a different issue from the current discussion.
HELOC accounts should be defined in Quicken as Credit Card accounts and NOT be activated for downloading if you get into this "paid off" situation.
Deactivate the account from downloading. That should make your register and all its transactions available again.
Make sure it's defined as Account Type = Credit Card. If it's anything else, create a new offline (manual) credit card register, transfer the balance and use it from now on.