Hi,
Thank you – that wasn’t the exactly correct solution, but it lead me to the right one.
1. I had “Event” box checked in the post types – BUT I had the ReLabeler extension installed, and had renamed Events to Workshops (throughout the site).
2. I uninstalled the RELABELER extension
3. Unchecked the “Events” post type, refreshed and checked it again
4. Voila – save button appears beside tickets in the Event edit page.
So, the issue is a small conflict between the main Tickets Plus plugin and the Relabeler extension.