Has anyone had this happen?

So two days ago I took a FRER and it showed a light line possibly not even there. Then it dries and I look back at it last night and it’s a strong positive. My test from the night before that you can see the evap but no color even though it is dry. Still getting negatives today and yesterday morning. Was it just a weird evap or a faulty test? Has this happened to anyone with FRER? I’m just confused because I’ve never seen a dry test come up so positive with color. Thanks!!!