OK, this seemed to be an issue with my templates from 5.0.1.
I needed to run the following:
$ su - zimbra
$ zmprov in
wiki@yourdomain.com
$ zmprov impn
wiki@yourdomain.com /opt/zimbra/wiki/Template Template
# need to restart mailboxd
$ zmmailboxdctl stop
$ zmmailboxdctl start
Clear browser cache, and check.
Thanks to support for getting this to me.