No idea, but it happened to the two apricots I planted in my yard in year 2. I am in the northeast, near Boston. Trees had buds, opened leaves, then wilted and died mid-spring last year. One of the roots sent up shoots afterwards, but the other did not and stayed dead. When I dug them up this spring to replace with jujube bare roots, the roots from the apricots looked fine.
I’d like to try apricots, but I’m not going to bother with something that commonly dies for no good reason. Plenty of other fruit trees to choose from.