Adding one more data point for anyone else who finds themselves here:
I tried making a brand new project and tried to build the bare minimum to get this to happen again, and couldn’t get it to happen. I made a new GameInstance, a new Common UI widget, and had them reference each other the same way as my “real” project and… no problems at all?
So yeah, I have no idea. I really only wanted the native controller support from Common UI, but I think for my next project I’ll roll my own solution as this plugin is clearly unstable.