Ivarfigs,
Sorry it is not an answer to your question but rather another case pehaps similar to yours.
My potted Quarterpounder and Excell 3yr old showed some breba (a dozen each tree).
Some brebas fell of in May, other breba survivied till June, and grew to 3/4 of full final size then wilted and dropped off.
Interestingly, I observed for the past week that the youngest leaves just initialized ones, on both of these trees were faling prior to breba fall-off.
The trees must have felt stress of some kind. But main crop embryos are developing non the less.
At the same time LSU variety next to the previous two trees in larger pot is holding breba nice and green and is showing main crop too.
Only difference would be the size of pot and less heat on the third tree.
wonder if others have observed something similar already!