Yes, this has happened to me. I tested at 11DPO with Confirm and had feint positive. Tested 2 days later (13DPO) with another brand (Can't remember which but it was the pee in a cup then dip a stick kind) and it was negative. Tested later that day and still negative. Used Confirm again at 14DPO and it was a BFP.

Try Confirm again. I've got my fingers crossed for you.
Debbie