Failed to ovulate with first opk.

So I got 2 positive opks last month one on cycle day 13 but then I didn’t ovulate and then got another on cycle day 20 and did ovulate. I’ve been off the pill for 2 months now so that was my first cycle. Is there a chance that I could ovulate on cycle day 13 and this month was just a fluke? Has this happened to anyone else? Had anyones peak days drastically changed from cycle to cycle?