Faint positive FRER, negative clear blue digital

aF due tomorrow, got faint positive with FRER on 7/11, negative on clear blue digital. Retested each day since and FRER still faint positive (not getting noticeably darker) and yesterday still had negative clear blue digital.

Should I be worried about possible chemical? Pic below to show FRER tests. I actually think today’s was faintest (using FMU).