I've done the filter under "All",

I've typed in the specific invoice number, I've expanded the date range to include several years just to see if the open invoices I have would show up.

Nope, not using a third party system.

No payments have been received against the invoices. 

I had a payment like this last month, and there were no problems matching them up, but suddenly this month the invoices are not showing up in the "Find Match" screen.

It's a system problem not an Accounting one.

But thanks for your insight! I will just do a work around because it's just getting annoying.