This is from a customer. I’m at a loss. Anybody have an idea of what could be happening?

“I have an Early Elberta peach tree that the fruit seems to have frozen in time. They have grown to about 2-3” in diameter and now have stopped. Last year we had a wonderful harvest from this tree about this time of year, so I know it’s capable. I’m wondering if there is something wrong with the soil? Last season, about 15’ from this tree a plum tree did the same thing. The fruit grew to about ¾ there mature size and then just stopped. They even hung onto the tree past leaf drop in the fall. Very bizarre!
This is not a case of needing to thin the fruit for them to get larger. Things are just stopping! I can handle small fruit, but they never ripen! Please help!”