This ones a bit hard to call... how's your ph? Can you see any signs of a bug on any leaves? Sometimes certain fungus can cause that circular damage also.
I'd go in and remove the affected leaves the best you can and check for any pests. Double check your ph is accurate (maybe recalibrate the pen if need be), and then possibly look into doing a neem spray. I know that's a pretty broad group of answers but hopefully you'll get to the bottom of this.✌️