I have found the FRER (the white plastic ones in your second image) to be accurate everytime, I have never heard of false positives on them, but I do know the indentation line that you speak of... I have pulled way too many apart to inspect closer... however a pinkish line is positive... even if your period arrives on time, it might mean that there was the very beginnings of pregnancy that didn't stick, so maybe they aren't false positives??

Have you tested again since these images?