no, dont change your chart.
i just thought maybe when you put your 'P' on your ff chart, that perhaps you were off a day or sumthing, like maybe when you put your P in for cycle day 15 and 16 that it was actually day 13 and 14 and you just made a mistake. (like thinking its tuesday when really its monday)
it is weird though
it detects lutenizing hormone and its odd that it is detecting the surge after ovulation has occurred.
i dont know if you are using the paid version of FF, but if you are, maybe search through charts that use the fertility monitor and see if that is a common occurance.

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