OK, I think I have an idea what might be going on. On FreeNAS 11.3 I was using a Z-Wave.Me stick with your custom_devfs ruleset method. On TrueNAS 12.0 the same stick was giving the problems described above. However I happened to have a Aeotec Z-Stick Gen5 in my ‘tech drawer’. In desperation I plugged in the Aeotec device and bingo, cuaU0 was back and I could start a Z-wave network in HA. The only difference I can think of between those two sticks is that the Aoetec is gen 5 and Z-Wave.me is not. Is it possible that there any difference in the support for pre gen 5 devices?
Anyway I’m going to rebuild the network based on the Aeotec