Hi Tom,
I tried to create module but it still did not show.
Do you have a backup of your site in J! 3.9.18? pls share with me via email: sales@joomlart.com , I will try to update Joomla from my end and see how it goes.
As I mentioned above, I tested with quickstart package of this template by upgrading Joomla latest version for it but all modules still display properly.