Positive test then negative tests

Hi all,

We’re in our 9th cycle of ttc. Had a CP in July and my cycles had been messed up since until last cycle which was exactly 30 days. Now 3 days late on this cycle. Did a cheap test on day period was due and was a clear positive (pic attached)! Did a clear blue the next day and definitely negative. Did I get a dud test, the first one? Line showed up within about 3 minutes.

I’m worried it’s another chemical 😣

Edit: I have now tested with a FRER, which was also negative 😔 any ideas?