Comment 4 for bug 1651735

Also occurs on Zesty installations that have been upgraded from Yakkety.

Unity8 fails to launch (classic black screen) and unity8.log shows the error:
"character conversion failed"

This is due to incorrect multiple versions of boost being present on the system because they aren't removed when upgrading.

Counted 6(six) different boost versions installed in Zesty because of taking the upgrade route through multiple Ubuntu versions.
'apt-get remove --auto-remove --purge' does not remove them so looks like a genuine dependency resolution problem when upgrading.

Manually removing all the old boost versions works around the problem and allows Unity8 to work again.