I am having the exact same issue. I have a C-7 Hub and have been regularly updating the platform software (but not Z-Wave firmware). I am now on Platform version 2.3.8.140. I followed the instructions (but did not downgrade to 3.3.8.122).
I get an error 404 after trying to install zipGateway718, but if I go back to zipGate715, everything is working fine.
Run the endpoint to install the 7.18 multiple times until it tells you that it is already updated. Then reboot. If that does not fix it, leaving it on 7.15 for now wont hurt anything.
If Z-wave keep crashing, then try running the zipgateway718 endpoint again, wait for it to finish. Then run it again until you get a message saying it is already updated. Then reboot. It seems to take multiple runs for it to take for some people.
Thanks JTP, I tried but it failed. I had to go back to 715, reboot and had to install zipgateway 718 twice, before it reported the proper version.
All is well now