After six long years of struggling with Ant+ issues that just wouldn’t go away, I have finally stumbled upon the solution quite by accident: replace the PC!
Almost all of my Ant+ problems have been solved, anyway. My Kickr v2 still disconnects fairly often, but I use my Assiomas as my power meter, and I don’t generally notice if the trainer loses a few resistance changes.
I wonder if the solution to this lingering issue is simply to replace the Kickr. (Sadly, I no longer have the CycleOps trainer that I started Zwifting with, to see if that works with the new PC.)