Ah yes, I can understand why that is happening.
The Power off activity is a virtual activity that just shuts off the running activity for the hub it’s associated with. ( That’s why you technically can’t turn those activities on)
Because it’s a fake activity, it has a fake Id and I use those IDs to stop duplicates being created. This means the second hub tries to create a power off activity with the same Id (-1) as the first and smartthings don’t allow 2 devices with the same Id.
I will fix this next time I work on the driver, thanks for pointing out out
You should still be able to create an automation to turn off the current activity if you need it before I get around to fixing it.