Sorry to hear you are hitting difficulties.
It seems to work for me on a clean test site, I’m not sure why it might be failing on your own site.
Have you applied any category/tag filters to the widget and could it be no matches are being found amongst the upcoming events? If so, does clearing those filters help?
YES, I’ve deactivated all other plugins to check for a plugin conflict.
YES, I’ve reverted to the 2011 default WordPress theme (with other plugins still deactivated) to check for a theme conflict.
Thanks for giving those steps a try. I’m puzzled because – as noted – under default conditions (see our full post on testing for conflicts) I couldn’t see a problem.
Just for the avoidance of doubt, can you confirm if these steps enabled you to identify any conflicts?
Thanks!