called "bud balling" or "bud drop". the buds form but turn brown and drop unopened. common in tight, double-flowered cultivars with heavy petal count, less so in more simple flowers with fewer petals. is yours 'betty sheffield supreme'? buds remind me of that one. balling can be caused by too much or too little water, nutrient deficiency, poor drainage. sometimes mine do that when the weather goes from typical late-winter mild and cool (peak japonica bloom period in alabama) to a very warm spring quickly. i think the heat disrupts their flowering cycle. this issue is not as common in my area as some other places from what i have read (mentioned in the link below).

bud drop

Big temperature drops is the usual problem for me. We had had a mild winter and temps then went from the 50-80s in Dec/Jan to 19. Except for one bloom in one japonica, I lost all blooms in all the japonicas this year... Have never had this happen in 12 years! The sasanquas were obviously not affected since they had already bloomed.

Could be temperature related. I'm in norcal and we got tons and tons of rain but my camellia's did fine.

I have had years with bud drop before opening and I think it happens when the temp drops too much during a certain part of bud formation.

Did you have any colder than usual weather this year?