Not sure, but the same thing happened to ours last year. We did have a lot of rain a few days before, so the only thing I could think was that it 'drowned' if that's possible.

Shame, it was very pretty, but I was put off getting another one.

Did you get yours in HD?

Check around the roots for vole damage. Voles (not moles) like to chew on plant roots.

Wish I could help, but I am clueless, as the same thing happened to my white-berried Beautyberry shrub last week and to a mature, ten-year old, Hypericum last year, just as it was starting to bloom. UFO's?
Hope someone has a logical answer. I suspected that the thief(thieves) who went halfway across my rear garden to lift two Banana trees had an urgent call of nature and the Beautyberry was handy. Oh well, lose some and lose some more.
Rb