Everyone else that posted all had some great points - read what they have to say and then look at your breeding practices a little more closely.
You obviously have a fair idea of what you are doing if you bred out some Cinnamons last season.
It sounds like the major variable is the male since I assume you are attempting to pair him with proven females. If he is getting stressed out by the change from his tub to the female's tub he may not perform.
There are a number of tricks you can try (some of which have already been mentioned). If he seems stressed out you could try shortening the time that he is in with the females.
A few other things that seem to jump start slow starters:
Put two males together (monitored and only for a short duration) they may "spar" but so long as you are monitoring their interactions and are able to intervene no one should get hurt. Competition is what drives most animal behavior, when we bring these snakes out of their natural habitat we essentially remove all competition. This has it's ups and downs, but can help during breeding season.
If you feel uncomfortable with this you could try putting the shed skin from one of your other (sexually mature) males in with your YB male and his female companion. Just the scent of another male is sometimes enough to give the illusion of his presence and spur that competitive drive.
Never underestimate the power of misting your animals!! This is a big one for me. Pairing your sire and dam together during storm fronts is fine, but adding the little extra realism of some mist goes a long way. I don't see this tip mentioned too often, but for the buck fifty I spent on a water bottle it is by far the most useful tool I've purchased.
Try to maintain as natural of an environment as possible in the room that your racks are in. (I know, racks are no where near "natural", however I am speaking mostly about the lighting and heating issues.) After it is dark in that room do your best not to turn any lights on, if you must enter the room try to use red lights so you don't disturb the animals so much. Also, if you drop your temperatures at night try to set the timer so that they do not drop until after it is dark and or raise until after it is light. Follow the natural season change as closely as possible. These snakes may have spent their entire lives in captivity, housed in a rack, but 99.99% of their behavior is still hardwired from millions of years of evolution. They are still wild creatures that expect certain "rules" to apply.
Do a search on this and other forums for breeding tricks and tips, even tips that are generally applied to other species can sometimes work. Try Google and look at some of the breeder sites on the Breeder Listings section for more ideas. A lot of the information will seem redundant, but every now and then you will find a pearl of wisdom.