I have a few Dovyalis seedlings, some in a greenhouse and some outdoors (it's San Diego). They all seem fine except one D. hebecarpa, which seems unhappy about something. It is growing, but it has bouts of leaf drop: some perfectly fine green leaves just fall off, and occasionally the tips of the new branches dry out and die. I inspected it for any visible pests or anthracnosis-like wounds multiple times: there aren't any. What is it unhappy about? It's in a greenhouse. Whatever it is, it doesn't seem very infectious, as the neighboring plants show no signs of it, and other Dovyalis seedlings seem fine. It's more like it's just unhappy about something. Any ideas? Thanks in advance!