I'm using a GE z-wave plus 3-speed fan control configured via Group Association to control 4 GE z-wave (non-plus) 3-speed fans. This works great from the z-wave plus wall switch but not via the hub.
Use the wall switch of the z-wave plus fan to turn the fan on, off or change the speed and all 5 fans work in unison.
Use the hub to do the same and only the z-wave plus fan reacts.
Scenes look like it could be a good alternative.
That turning on the Plus fan controller does not respect the already established association is strange. Perhaps @mike.maxwell could comment.
You might want to try installing the basic Zwave tool driver from the Hubitat Github repository. Temporarily change the driver for the fan controllers (I would do this with all of them) and run the association report and watch the logs in a new tab.