Pink line but then disappeared

Hi ladies,I did a frer this morning and after it started developing the area where the 'pregnant line' should be went really pink in a vertical strip. I got excited but then noticed it fading, until it was gone completely!
Anyone know what this could be? Do you think it could be that I have a very small trace of preg hormone and it was picking that up?
Attached is the test (I didn't manage to get a pic of the pink second line when it was developing)
Appreciate any thoughts or comments 😘

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