SST method mysqldump does not seem to work at all.
WSREP_SST_OPT_PORT is set to readonly first when --address is processed, and then again when --port is processed. The second attempt fails, and so does the whole script. I don't see how it can be avoided, maybe it doesn't happen when it runs on the default port.
It seems to have been fixed in 10.2 in the scope of