BFP/BFN/Evap??

So. We have been ttc for around 8 weeks now, and currently I’m either 12/13dpo with AF due tomorrow. The top test is from yesterday afternoon and the bottom test is from this morning with FMU. Bottom test is clearly BFN, but the strangest thing happened with both of them. I’ve never had a BFP before on any test, and when I took both of these immediately they showed as faint positive and then faded to negative after about 5 mins. And then the top one reappeared very faint but there is colour in it. Bottom one has stayed BFN. Anybody else experienced this?