How long have you had the said plant.
It maybe that the soil/ leaf mould has built up, covering the roots. If they are too deep they will not produce flowers. The cold snap at the end of March and thru April may have had an affect. Look to see if there were tiny buds that have refused to develop due to conditions.

Hi Jenny

Have you got it in the right spot , full sun at least 6 hours a day not crowded out by other plants well drained soil and fertile enough to give it the energy to flower they are greedy feeders.

It may be planted too deep ? this stops it flowering as well

I plant about 1 1/2 to 2 inches under the soil , if me if you want to move it March/ April I find is best with a established plant and helpful when dividing the plant as you can seperate out all that have new growth just about starting to grow but if bare rooted I try and plant in the Autumn warm soil and wet helps the roots grow away quickly which you may wont to do if not seperating .

Peonies hate to be moved but if needs must I would

Gg

I planted 2 dry bare roots of Sarah Bernhardt right on top of the soil a few weeks ago. Only barely covered. One of them sprouted quickly, and has made a bud that I do not think will flower. The other has made quite good top growth as well. I think this points out the importance of shallow planting to encourage flowering. You can always pop a bit more soil over them while hoeing but not too much.