Answer: Based on your description it is difficult to identify a definite cause of the problem, but here are a few possibilities. Drought stress can cause the symptoms you describe, and insects also can cause buds to be deformed and fail to open.
Roses need a rich soil and regular watering to keep them evenly moist but not soggy, so it is possible that there is a soil problem. Container plants are a challenge when it comes to watering, sometimes needing it twice a day on very hot, dry, and windy days or if the pots are too small for the plants. You might see if the texture of your potting mix has deteriorated over time; or if it has been allowed to dry out, it may require some care in rehydrating it thoroughly. A top-dressing of compost is helpful for all roses, and you might also consider fertilizing (either a timed-release granular or water-soluble type specifically for roses) according to package instructions.
Finally, inspect the blooms very carefully for signs of aphids or other insects. Japanese beetles may be burrowing inside the blooms, as might thrips, which are so small they are nearly invisible. A sharp spray of water from the hose will knock away aphids; handpicking or using a neem-based spray will take care of the beetles, and insecticidal soap used according to the label instructions may work on the thrips. The soap also is effective in case of a serious infestation of aphids.
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