First Signal evaps or chemical?

Katie • My name is Kate and I just gave birth to our beautiful daughter February 17th 2016. She is our world and we couldn`t feel anymore blessed❤ I am currently pregnant with our July 2018 baby!
So this was taken yesterday with FMU. The problem Im having with these tests is while I see a shadow of a line within the time limit and I come back several hours later to something of this sort. This has happened 4 days in a row except for today. Todays doesn't have a hint of anything. So Idk if its just the test or Im having a chemical. I realize you are to void the results after the time frame but, I just find this odd. Anyone have any insight? I had a chemical with my first pregnancy and then the following month got pregnant with my daughter so I have experience with fading lines...just not this brand.