I finally got it set to a static address on the preferred subnet where hopefully it will never have to move again.
I then found that if I connect both the Hubitat hub and also my Hue Hub (same subnet) both to a managed switch, they cant find each other. I did find a post about this already, so I am not the first to realize this. I dug up a 4 port unmanaged switch, plugged it into my managed switch, and plugged both the Hubitat and also the Hue up into the unmanaged switch... Hubitat was then able to find the Hue hub.
It just seems like Hubitat wants to run on a very simple network (unmanaged, no extended subnets), which is somewhat counterintuitive to a lot of power users with managed networks I would think.
I have worked around it however. It's not how I wanted to do things, but it was resolvable. Live and learn.