Question: FRER Disappearing Line

Hi all!

Yesterday I took a FRER test at 9 DPO (yes, I know it's early but I have experienced a + at 9 DPO previously). As the test processed, I saw a greyish line appear within 3 minutes. It was very faint but still enough to be seen in a photo.

About 3 hours later, the line was no longer visible.

Today, at 10 DPO, I tested again and got the same result. There was a faint grey line within 3 minutes which had started to fade a few hours later.

I had some expired FRERs in our bathroom from 2014 which did NOT produce any line of any color.

My husband recommended opening one of the newer tests after it dried and putting a drop of water on it. Again, the grey line returned.

My questions are.. have the tests changed?

Can a faint BFP fade as it dries?