Bfp and bfn, same test, SAME PEE?!

I got a BFP with my FMU which I peed into a cup.

I wanted to test again to be sure but I was out of tests! So I left the pee cup on the bathroom counter (under the AC vent) and ran to the store to buy more tests. I was probably gone for 30-45 minutes tops and then returned with 2 more of the exact same tests (FRER). I dipped them both in the pee and they BOTH came out stark white negative!!! WHAT IS HAPPENING?!? Did the HCG evaporate out lol!? Did the first test absorb it all? I need answers😩😭