have you replenished the soil in that time? do you feed the plant? if the answer is no to either or both then I suspect that is the problem. having said that mine haven't started to produce buds yet so it could just be you are expecting them earlier than they emerge.

give them a feed and repot next year in a bigger pot with fresh compost or cut the clump up and repot so you have extra plants.

Soon after I posted here a month ago regarding my Agapanthus which had no buds I now have a good dozen which will soon open up. I did give them a feed though and keep them well watered.

Perhaps, John, you should feed yours pdq