Prunus mume are one of the species that respond well to partial defoliation, which really aids in ramification as they tend to grow rather linear.
Plus I know that Brent holds his cuttings for longer periods of time to attain better root development prior to selling. They are a species that require more stabilization before shipping, changing climates and transplanting. Particularly when they are young. The young plants appear to do well even with less established roots until something changes, and then they do not have the reserves to cope. For this reason experienced growers like Brent give the cuttings extra time before selling.
Both of the above reasons increase the chance of recovery in situations like yours.
The Chojubai are just a fickle species, whose first reaction to any change is to lose their leaves and pout for a bit!
For both species I tend to use the same approach to stabilize new arrivals and young stock. Deeper substrate on the acidic side with a bit higher moisture retention. Partial shade protected from wind. Less frequent repotting particularly for younger stock and I do not begin regular root work until after year three. Full sun this time of year in your location will probably be fine.
Michael Hagedorn has written a number of good articles on Chojubai and they can be found in the archives on his website.
. Good luck with yours!
