Once a year or so Galera on one of my 3 nodes breaks down and in the log you can find something like:
Failed to open channel ... State not recoverable
In my case, I end up with a empty gvwstate.dat file and that’s the problem. I delete the file and restart MySQL, then Galera syncs with the other nodes and everything is fine again.
Link to another article: https://github.com/codership/galera/issues/354