Heat.

IME with DD is that it thrives on heat (moist eastern type heat, not western desert-dry type heat). Bud formation and color is so much better in our typical hot, humid summers. than at any other time. Some people report the colors fade in strong sun, but I've never noticed that in our humid conditions

For the OP: have you been checking for thrips? Thrips can cause various types of bloom and bud damage depending on what stage they infect the plant. They can cause buds to deform or to not open properly..

Well it can't be because of heat because mine is doing the same thing and it's been cold, wet and gray here for most of the spring. We've only had sporadic days of 80 degrees and sunshine. For the most part it's been gray, drizzling and in the 60s. One of my DDs is covered in wimpy, flopping stems with small, flat, formless and, for the most part, colorless blooms. The other one just refuses to bloom at all.

Of the four roses I planted, DD is doing the poorest. It was a young plant and got sprayed with a lot of deer repellant when it was young. If it doesn't shape up by the end of the season, I will replace it with another DD next winter. I've had excellent luck with DD in the past in the same garden.

There are many reasons a bloom may pancake. It's just that at this time of year, heat is the most likely suspect. The growth and nourishment normally required for the bloom is short-circuited by the tremendous pressure on the bud to open. Lack of water can excerbate this, too.

St. Patrick is known for being hugely heat-tolerant, but under the right conditions during high-heat, its blooms will pancake with consistency. Double Delight is another one I've seen do this. Mister Lincoln will do it, too.

Some roses get smaller under heat stress, some pancake, some do both.