10.1.31 does not join any Galera cluster with SST xtrabackup-v2.
To reproduce: Start a 10.1.31 node and wait it to connect to a cluster, it won't, timing out at:
The Donor does not receive the SST request.
Workaround: use wsrep_sst_common and wsrep_sst_xtrabackup-v2 from versions < 10.1.28.
Scripts from 10.1.28/29 can't be used as they have other bugs.