Has it been warmer than it was before? Bucks can temporarily become heat sterile. If weather cools off it can take up to 45 days for him to become fertile again. I checked the temperature in your location and it has been 92F/33C recently. For my rabbits that can be enough to cause bucks to lose fertility, but this varies by rabbit, and type of housing. My rabbits live outside, and I stop breeding during our two or three hottest months, and mainly breed in spring and fall.
The other common things that can cause infertility in rabbits are age (more than 4-5 years old) or obesity. Rabbits can keep a lot of fat inside their bodies, so this may not be easy to see until it is pretty far along.