Hi Giles,
I’m sorry to hear you’re running into this issue, but I’ll be happy to help you get it figured out!
First, it looks like you are running an older version of Event Tickets Plus (4.2.4). Can you try updating to the current version (4.5.4) and see if that fixes the issue? While you’re updating, I’d also recommend updating Events Calendar Pro (to 4.4.17) and The Events Calendar (to 4.5.12.2). If you don’t see prompts to update in the Plugins section of your dashboard, you can do so manually by following these instructions.
Let me know how it goes!
Thanks,
Jennifer