I experienced similar problems. In fact, I have experienced similar problems on every openHAB upgrade since the move to 2.5.
I ultimately moved to a new Z-Stick, but this didn’t resolve my problem either. Make sure your network has no dead nodes and all of that. Once you have a clean, well routing network, the issue can still occur (it does for me). To resolve I have to shut down OH2, remove the Z-Stick from USB, wait a good 10 seconds, re-insert the USB, then start OH2 again. This usually fixes it. If it doesn’t, I can sometimes just remove the Z-Wave binding, remove the USB stick, wait, and reinsert it, and then re-install the binding, and the issue resolves. Sometimes I have to do this 2-3 times before I get it working. Once it is working it’ll stay working without any issue until the next OH2 upgrade/restart/system reboot, at which point I likely have to fiddle with it again.
As I’ve had this problem across multiple controllers of differing brands, I’ve chalked this issue up to my physical hardware, my Ubuntu installation, or a binding bug.