Wrong reference date for plugin components

To view all the events of our club on our website, I use the plugin Events Manager and additionally the plugin WP FullCalender to view the events in a monthly view in addition to the events-list. Events Manager has been working fine for a long time. Since a few month time seems to stand still for the plugin Events Manager as long as I don’t log myself in to the backend of our website.

Yesterday was March 4th and I was last logged in to the backend of our website. Today morning I opened up the Frontend of our website. In every events-list on our website (landing-page under the headline “Termine”, sidebar on http://www.laufgruppe-dresden.de/trainingszeiten/ and http://www.laufgruppe-dresden.de/kalender-termine/kalender-monat/, main-content area on http://www.laufgruppe-dresden.de/kalender-termine/) the event with the date March 4th was still visible. The small calender in the sidebar of http://www.laufgruppe-dresden.de/kalender-termine/ also showed March 4th as todays date. Only the big-size calender in the main-content area on http://www.laufgruppe-dresden.de/kalender-termine/kalender-monat/ showed March 5th as correct todays date.
All the named events-lists an the named small calender in the sidebar are elements of the plugin Events Manager and obviously refer to a wrong todays date. The named big calender which showed the right date is an element of the plugin WP FullCalender, which enhances the plugin Events Manager (Description @ WP FullCalender plugin page: “Integrates seamlessly with Events Manager”).

After viewing the Frontend of our website and noticing the inconsistent content within the Events Manager elements I logged in to the backend of our
website. I did nothing more than just logging in. No changes, no saves, nothing. This was enough that somehow the Events Manager plugin updated its reference date from March 4th to March 5th. In any events list the event from March 4th wasn’t visible anymore and the small calender in the sidebar showed March 5th as todays date. But it does not do this automatically. I always need to log in to the backend for this.

I have not changed anything in the files of the plugin. I just use the placeholder file eventcategoriesimages.php and the template file events-list-grouped.php as child-plugin-file as described in the documentation of the plugins website. Using the plugin without these child-files had no change in the incorrect behaviour.

I hope I described my problem understandable and someone can help me. Thanks already for that.

The page I need help with: [log in to see the link]