Pineapple Quince Mystery

I have a 5 year-old Pineapple Quince in my orchard. All indications point to it being a healthy tree. During the growing season it receives about 10-12 gallons of drip irrigation at the drip line. Last growing season was the second year that it has borne fruit. But something strange happened last year. Mid-season, when the fruit were about the size of a golfball, they all started to drop; not one fruit made it to harvest. Our other quince, an Aromatnaya Quince, which we care for in the same manner, delivered us a bounty.

I’ve asked around and scoured the internet for a possible explanation. Does anyone have any ideas about why the Pineapple Quince did this? Thanks in advance.