custom link problem

Hi. I have recently installed an event manager plug-in in WordPress. The plug-in is working correctly for the most part. However, I am having a problem.

For the EVENTS page, I added a CUSTOM LINK to my main navigation. The page displays properly on a full screen. However, when the screen is small (on any device), it is not possible to click on the HAMBURGER or the links in the calendar (Sunday October 18).

The other pages do not have this problem. As I said, I added this page as a CUSTOM LINK per the instructions of the plug-in author.

http://upstairslounge.net/z1/events/