After upgrading from a joomla 2.5.x install with JEvents v3.1.39 to a joomla 3.5.x install upgraded to JEvents v3.4.50 and all categories and events are gone. I have no idea where to search to fix this. In de database I see that all the tables are there and filled. Adding a test event shows up in the table also, but in the backend I see only the test event, no categories or events.