I have found an incompatibility between Event Tickets and Uncanny Owl Learndash Group plugin.
When both these plugins are active it is not possible to add Tickets to new events. The Tickets form in wp-admin when creating a new event is greyed out.
Oddly it is possible to add a ticket to an existing event which already has a ticket attached. However, if you delete all tickets from an event you cannot add a new one.
I have also raised this issue with Uncanny Owl. I would be grateful if you could help resolve this along with them.
Here is a link to the plugin I am referring to https://www.uncannyowl.com/downloads/uncanny-learndash-groups/