First off - nice pictures! Kiwi is still somewhat infrequently grown in our area and so we don't have a lot of experience with this fruit, but if you'd like to take a look at this excellent OSU publication https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/pnw507.pdf you just might home in on the answer.

It indicates a few possible reasons the tissue may be blackening. One is from verticillium wilt, a soil-borne fungal disease prevalent in our area. Supporting evidence for this might be if you've had similar issues with strawberries, black raspberries, potatoes, or other crops in the Solanaceae family in the area.

It goes on to say that kiwi are also are sensitive to root knot nematodes (Meloidogyne spp.)

Culturally speaking, they can be very sensitive to over-fertilization and that they need lots of water. (I think we can rule that out this early, wet spring.)

I hope this publication helps to shed a light on the problem and gives some solutions. Otherwise, keep taking good care of the plant and continue to watch the problem.

Thanks for the quick response Erika and the reference document. Very helpful. The growth on these vines so far this spring has been tremendous, and we really haven’t had a good rain in over a week so I’m not ruling out water.  The fact that the younger ornamental vines showed the issue first, which budded earlier than the more mature fruiting variety, I’m hopeful that turning on the irrigation system this w/e will curb the issue. I’ll write back with an update.