Positive Opk on time but period early

Hey all-

My ovulation and period almost tracks exactly to the day as predicted on my glow. This month’s OPK test was positive on the day as predicted. However i started bleeding today. What was cause my period to come 6 days after my positive OPK?

It was just some spotting on my underwear but when i wiped it was definitely more so i doubt the odds are implantation bleeding.

Anyone experience this?

Thanks!