Calendar widget events not highlighted

Hi all,

I am using WP Full Calendar and Events Manager.
My theme of the homepage is Sydney in the theme of the WP Full Calendar is black-tie.
The full calendar works finde. The widget is different to that on this site: https://demo.wp-events-plugin.com/shortcode/
The design is different and my biggest problem is that only events higlighted which are on the first date of this calendar page, by example Monday the 26th September.
Another event on the 4th and 5th October are not higlighted. I can click on the 4th October for going to the event but not on the 5th October and nothing is higlighted, too.
I changed the WP Full Calendar theme but it does not has any effect to the calendar widget.
What can I do to higlight my events in the widget?

Thanks