The Xenial failure sounds very much like bug 1592669, which looks like it was fixed post-Xenial and hasn't had a fix backported (it's somewhat invasive but probably SRU-able if done with care).
The Xenial failure sounds very much like bug 1592669, which looks like it was fixed post-Xenial and hasn't had a fix backported (it's somewhat invasive but probably SRU-able if done with care).