Hey Malcolm,
Thanks for going Pro and welcome to the forums!
I’m sorry you are having this issue, let me help you with that.
As a start I would like to ask for 2 things:
1. Could you share with me a screenshot of the setting of that widget?
2. Could you possibly run a test for conflicts? Basically what you need to do is switch off all plugins except for the Modern Tribe ones and switch to a default theme like twentysixteen. Then check if you are experiencing the same issue. Here’s a neat guide for the whole testing: https://theeventscalendar.com/knowledgebase/testing-for-conflicts/
I’ll be waiting to hear from you!
Cheers,
Andras