Cleaning Autoptimze cache does not help. However, when I deactivated Autoptimze, the events are shown fine!
I did not find anything on their forum about this issue. Until I find a solution, I will keep the plugin deactivate for now.
That’s a bit curious. I have two sites running with The Events Calendar and Autoptimize without any problems. On your site the plugin is creating the correct HTML structure in the mobile view but for some reason the PHP isn’t being interpreted correctly in only that section. Maybe there’s something strange going on between Autoptimize and W3 Total Cache?