Your template is using Bootstrap 3 which is newer than the official Joomla version of Boostrap 2. The more sophisticated template developers doing this like JoomlaArt have created a workaround script to avoid this problem but the smaller template developers have missed this issue and workaround
We have implemented our own workaround in JEvents but our latest released version didn't work for all templates. Can you try this solution - unzip and upload this file to components/com_jevents/assets/js/jQnc.js and make sure you set the JEvents config option to fix jQuery issues on the first tab of the JEvents config