The usual answer to this is too much nitrogen, but if you have used the same growing methods in the past with good results then...?

Maybe they just take a lot longer. Definitely not excess nitrogen

Heat could be the problem, Rattlesnake take the heat better than most varieties, they should start producing once it cools down. I have the same problem here with most of what I grow when it hits the upper 80's. Thankfully that doesn't happen often.

Annette

Here in Oklahoma I wouldn't bother growing Kentucky Wonder as the variety is sensitive to our hot, dry conditions. That may be true, also of Blue Lake. Rattlesnake, however, thrives in those conditions.

If you can keep those beans healthy until the heat passes, you may get a good fall crop.