It seems that update can fail on some environments due to Galera sync timeout being too short. We've seen the 360 second threshold broken and a failed update because of that, even though Galera eventually synced fine, clusterchecks OK and pcs status clean. However, it's worth noting that this problem has only been seen once so far.
This bug did not make the OSP 8.0 release. It is being deferred to OSP 10.
Could not reproduce. Please re-open if re-appears.