Due to changes in WordPress 5.0 and The Events Calendar 4.7, the way the automatic placement of the “Register” button and form has changed. If you are using a custom single-event.php file in your theme, try enabling this setting found on the Form tab:
This will cause the plugin to use the hooks ‘tribe_events_single_event_before_the_content’ or ‘tribe_events_single_event_after_the_content’ to place the registration form. Your custom single-event.php file will need to include these hooks.
