Nature hates me. Apparently I'm the last to figure this out...
I have 5 apple trees of various ages:
Mystery Apple - this was labeled a Pink Lady but it's not. It's a yellow-green apple instead of pink. This is the 3rd or 4th year I had it. It's probably 8 ft tall and my most mature tree. I got 3 apples from it last year. It was the first time it produced fruit.
Granny Smith - I purchased this tree locally 2 yrs ago. It's about 6.5 ft tall. It has never flowered or fruited.
Honeycrisp - I purchased this tree locally last year. It's just under 6 ft tall. It was loaded with flowers last year and I used it to hand pollinate the mystery apple tree. This year it produced lots of blooms, even though it really needs to focus on growing bigger. The deer seem to LOVE this tree though and they've nearly killed it this spring by eating over half the branches.
(2) Sugar Bee seedlings that I grew from store bought fruit last year. I put them in the ground this spring. They are doing great but still under 3 ft tall.
So what's the problem??? Well, I tried to hand pollinate the mystery tree and Honeycrisp because I wasn't really seeing any bees around. A few weeks later I noticed baby apples all over both trees. I was delighted but also very annoyed that the Granny Smith is a dud this year. Then the deer struck and wiped out most of the Honeycrisp. And because of all the rain, I didn't get to spray the trees in a timely manner based on bud recommendations. Well the fruit is now about thumbnail size so I decided to go bag it to keep the bugs out. I started with the mystery tree... I was dismayed to discover nearly ALL the fruit dropping the minute I touched it. I did manage to bag TWO apples but only 1 feels solidly attached to give me confidence of reaching harvest. I also noticed a lot of the fallen fruit looks deformed. Lumpy. Then I went to the Honeycrisp tree. It only had about a half dozen baby apples left on it after the deer raid. Same size as the others - thumbnail size. I noticed almost ALL of them were also deformed and lumpy.

I picked off all but the best two and bagged them.
So what would cause that? Plum curculio maybe?
Very disappointing