Question
I'm from Columbus, OH.  Have 25 KO's that have bloomed wonderfully for over 5 years.  This year I did the usual...pruned in the spring, fed, applied BAYER systemic in late May to deter Jap. beetles.

I had one good (not great) flush of blooms early in the season.
Then barely nothing.  I could see rose buds forming, but they never made a bloom, and just got brown.  I watered as usual.
Plants look healthy even now.k

Answer
When roses make buds and then they don't open but go brown, then there could be rose midges killing the buds on the rose bush. A rose midge lays it's eggs at the base of the bud and when the young hatch they feed on the inside of the buds. This damages the buds and so they don't open. Another reason coulod be that they re-acted to your systemic spray. For some reason Knock Outs don't really like sprays and some times they will re-act to them. J get a lot of questions concerning  their re-actions to certain sprays and Bayer is one of those sprays. The last thing I can think of is that although you watered, did the weather get extra hot or was there a heat wave, because that means the roses need lots of water and if they don't get enough then the buds will dry out.