This is weird to me, maybe not to someone else.

Towards the end of last season, one of my single oak leaf hydrangeas had half of the plant just completely die off, while the other half stayed totally healthy.

first picture down below, you can see half of a hydrangea, and the cut-back twigs of what was left of the other half.

Now, I have another hydrangea just a couple yards away has half of the plant wilting again. This is the same behavior the other showed before it died off (see second picture).

Very weird. Anyone seen this or know what the cause is?