""Resolved" meaning the amount does not show in accts receivable, and I've found a credit memo as well as a journal entry"

The JE would be the error, then. You don't use JE for AR, AP, inventory, QB Payroll, Sales Taxes, etc.

"that appear to be "correcting" the invoice (it should not have been set up as an "invoice" in the 1st place - the "customer" did not OWE the money).  I believe the reminder may have shown up when I installed Quickbooks 2014 (I'm now using QB Pro 2016).  It is like the reminders that are generated by QB (not ones "set up") - like bills to pay, checks to print, sales receipts to print, etc."

Let me try to explain what you might be looking at:

You open the data file and it is set to show you the Reminders List, because you selected this in Preferences. On this list, using Preferences, you get to select what to see as a List, what to see as Details, and When these things should appear, such as 15 days or 5 days from due date.

"I could stop it from showing up by checking the "don't remind me" under preferences for overdue invoices, but that would stop ALL reminders for overdue invoices"

I think this is all you need to do:

Run the AR Aging Summary report. This customer would be showing, with Total = 0. Double-click on their Total of 0. Here are unapplied activities. Double-click on that invoice. Use the Icon to Apply available Credits.

A JE is always a mistake for AR. AR is invoices, credit memos, or statement charges, and Receive Payments. Here is a different thing to do, to prove this:

Open Receive Payment for that name. Put in an Amount of 0.

You should see open charges, and at the bottom, Available Credit. You can cross-apply them, here. Or, using the icon at the op of the Invoice, as I noted.