Hey Ian,
I’m glad you reached out. The update from 3.9 to 3.10 was a big one as was the update from 3.11 to the current version of 3.12.
There are quite a few things to consider when updating, especially if you have customizations to the calendar. Do you have any of those? You can check by heading to your theme directory and looking for a tribe-events folder. It’s also worth checking for other installed plugins or functions in your functions.php file that may customize the functionality of the plugin.
The biggest change was that we refactored the code and updated namespacing. In other words, many of our functions and classnames that worked before are now deprecated and replaced with a newer name.
I would recommend setting up a test environment and checking from there so there is no interruption to your live site. From there, please do read the release notes for the last few releases since 3.9 to see exactly what’s changed and how those may have affected any customizations.
Sorry for the trouble so far, but please do let me know if this helps and if you have any other questions as you review the changes.
Thanks!
Geoff