Welcome to the JEM forum where users try to help other users.
If your JEM instalaltion was working fine before the update it may have something to do with the new layout. JEM 2.3.0 automatically uses the new, responsive layout.
Maybe the first thing you want to do is try out the old layout. In the Backend of your Joomla site go to Components -> JEM -> Settings -> Basic Settings and under Style, change the Layout Style back to Legacy (Table Style)
Does that help?
Please provide some more info about your Joomla version and PHP version and template you are using
Hello Ernst67, I tried that allready, but it does not work.
I use Joomla 3.9.16, PHP 7.2 and the Protostar template.
I worked before with JEM 2.2.3 and had an excisting eventlist, but after the update it never showed up at the frontend...