Not sure myself but maybe it's a water issue from last year. Did it get plenty of water on a regular basis? I'm sure someone with more knowledge will chime in soon.

Thanks for trying! The bed is by the house and is watered in our droughty summer.

Any other ideas?

A couple of things come to mind. First, the trees do not necessarily leaf out uniformly......sometimes they do it in stages :-)

Also, there are various reasons for stem dieback, which may not be immediately apparent. Green and flexible is not always a firm indication of viable wood underneath. How do the buds look on the top, leafless portion? Are they plump and healthy looking or dry and shriveled or brittle?

Regardless of the cause, I'd be inclined to be a bit more patient and wait and see what happens in a few weeks to a month. If nothing showing by June 1, I'd recheck for deadwood and prune out if confirmed. And be sure to sanitize your pruners when you do!

How is it doing now?

Well, I could not stnd looking at it any longer and cut back the offending branches which were lookimg increasingly nonviable. I am fearful this may be a gradual dieback so keeping a watchful eye.

I have quite a few trees and have never lost one. This year with the worrisome maple and the unexpected death throes of my Tricolor Beech, I am experiencing gardemer’s grief...

Thank you for asking....

With that stump right there I'd check around the bottom of the maple for honey fungus.

Embothrium, that is a terrifying thought..

Cercis, how often and much water do you give the tree? Do you water when the soi's dry or nearly dry?

I think it's a watering issue because my Autumn moon did the same thing last spring when it leafed out. During the summer before we had a big drought and it was stressed badly.