What is this line?

This was an hour after it dried I know outside the window. But there was a faint line in the same place during the time frame which I find it’s a super odd location. I thought maybe it was an indent but it’s still there. Which indents disappear. What is this?? Is it invalid? It definitely cannot be the place a line should form. It was there at 3 minutes in that location too. Are these tests Clearblue just terrible? It seems like every single brand now is awful. I didn’t trust it during that time thinking it’s an odd location but left it out to see if it’s an indent which disappear and then was gonna throw it away.