Positive that fades away?

Ok ladies I am 8dpo and I did a test to which it started to show an obvious line but as time passed the line faded away it took maybe 10 mins to fade I then continued to do one after another all three did the same obvious positive that faded to nothing what on earth is happening why would a test just fade I’ve heard of evap it when you leave it too long a line appears but this is a line straight away fading to nothing (remember the darkest line on the top test is the test line not control)