Any breeders have females that will not go into heat or males that will not mate?

Hello there... I was just wondering if any other breeders have had female cats that will not go into heat, or maybe have one or two heat cycles and then nothing and are not pregnant, or males that seem to have no interest in mating for a long period of time, though previously being a successful stud?
That is the situation I am running into. I think it is because I so rarely have a litter. Most of my cats are spayed/neutered now because I wasn't breeding for a while, I was fostering for local animal shelters etc. At this point in time, there are no kitties in our shelter, and no siamese in our area, so I thought the time was right to plan a litter, and keep my bloodlines before the queen is too old to safely have a litter. She is 3.5 yrs old. She had a litter when she was just over 1 yr old. She used to have regualr heat cycles, but doesn't seem to anymore. My male hasn't had a 'girlfriend' in so long that I wonder if he forgets what to do...lol....
Anyone have any ideas? They're all healthy, up to date on vaccinations etc...

We have a couple of female s that have "silent heats" , and we have one male that has to have a very non-agressive female in order to do what he needs to do....

Sometimes males are reluctant to mate with a female that's higher in rang which often happens when cats livet together for a long time, fertile females are almost always "the boss" and that can be a bit "scary" for the male. I suggest you let it take time. Sometimes vitamin E can help the female to get into heat.

Sometimes cats can pick up things we humans can't and therefor won't mate with the cat we intended them to mate, they simply sense that the comination isn't good or that the other cat carries "bad genes".