Ovulation took place on CD 16 and CD 17

Am

I am now on CD 22 - now 5 days after ovulation I get another positive - see attached picture.

I knew I was about to ovulate on CD 15 because I had an ultrasound and HyCoSy done and my follicle was already 17mm then.

Does anyone know why I'd have another positive OPK after ovulation?

Thanks