I have no experience with tomatillos. A couple of guesses come to mind.
Flowering fruits/veggies need pollination, and maybe they aren’t getting it-do you have plenty of bees in the morning?
Secondly they need nutrients 15 30 15 and trace elements.
Once they are ready to and start to flower, that extra Phosphorus is needed, the balanced 15 15 15 doesn’t do as well for these as it does for leafy veggies.
Plenty of bees and we have had our soil tested it is right on the money. Thanks! Maybe they just fruit later - much later after the flowers are gone??