My sister in law had that problem as well. Apparently, there is a certain type of ant that eats something off a peony to make it bloom. When the exterminator at her townhome complex sprayed, they stopped blooming.
Not sure what type of ants, or why they need them, but it was a factor for hers......
They are the same ants that herd the aphids onto rose bushes, small black ones.
That peony came with the house. I don’t know why but it bloomed well though heavily shaded. For a few years, that is. Then it stopped blooming so I replanted it. No blooms last year but it’s sprouting well this year.
I know nothing about this stuff so I’m just guessing at what might work.