Hello,
Do you notice any black on the stems or leaves at all? I have had buds die before fully developing also, but in my case it was paeonia blight. This a soil born fungus and usually is from poor air circulation and dampness.
I have sprayed the soil and growth tips as they emerge through the soil and cut off any stalks affected with the black and thrown them in the garbage. Making sure that I sterilize my pruners after doing this.
The crown should not be planted any deeper than 1-2" below the soil surface on deciduous paeonies or they will not flower. If putting manure on, may want to put it around the plant and not on top.
Hope that some of this is helpful.
Is it getting as much sunlight as the others. Hate to dig them up as they do not like disturbance that much.

No, the roots surfacing are not the cause. It's probably planted too close to the hemlock tree. Peonies need full sun in this area, and they don't like root competition from trees.

And it's not true that they don't like disturbance when they're unhappy where they are. Dig it up and move it to better soil and full sun. I once dug up a peony is April and moved it to a different garden, and it bloomed that June for the first time in 15 years.

Be sure to remove and dispose of the foliage in the fall. Do not let it lie. Do not compost it. The botrytis will winter over in peony foliage.