It's possible that this is due to something lacking in their diet. Vitamin A and Vitamin E are both necessary for breeding enthusiasm and success. These vitamins are added to rabbit pellets, but they are vulnerable to loss when in storage.
You could try adding dark leafy greens like dandelion to their diet for Vitamin A and wheat germ, wheat germ oil, or black oil sunflower seeds for Vitamin E. If you google Vitamin A for rabbits or Vitamin E for rabbits you will find more information. Don't go overboard with these supplements. Phase them in, especially if the rabbits have been accustomed to a pellet diet. All changes in diet should be made slowly. (I'm sure you know this, Jackrabbit, but these posts are also read by people new to rabbits, so I try to make my answers as complete as possible.)
They are standard Rex, Most of the ones I “bred” are over a year old and proven. I have 5 bucks, and “bred” 20 does. So each buck “bred” 4 does. The way I do my breeding now is like so. Take the doe to the buck, wait for 3 fall-offs to occur, then after 3 fall-offs leave them together for 24 hrs, then pull the doe out of the bucks cage and take her back to her cage. It’s the way I’ve had the MOST success with breeding in the past. Also I put “” around bred cuz they HAD FALL-OFFS but NO kits. Cosima, I’m terrible with explaining weather. Here is a screenshot of the weather on my phone today. This is usually the weather we have every day here in the summer time.