There is a big probability that depth of planting is not right ( planted too deep ) or they are not getting enough sun. Peonies would not look healthy if ph is out of ordinary.
May be you were getting blooms that summer only because the winter was colder than usual. Another thing was it bare root or potted peony? Some of the potted peonies are so tiny it could take 5-6 years for them to bloom. One of my neighbors shared one of their peonies with me and after 4 years I still do not have a bloom because I did not take it seriously and just replanted it - I guess it was small and planted at the wrong depth and I did nothing for preparing the planting hole.
Do they have enough water after bloom time to create the eyes for next season? Could be an option as well.
