Question: My positive line disappeared

I tested and had a faint blue positive line appear within the first minute. It stayed for hours but I just looked at it again (obsessing on if it’s actually there) and now I don’t see anything anymore. It was same size as the line in the control window it was just much lighter so I’m confused because I thought Evap lines would stay after the test dried and that it wouldn’t show up during the reaction time.
Anyone else had this happen? What could it be