Hi there, @unterwegsinberlin,
The most common cause for job listings not showing up on the jobs page in WP Job Manager is a JavaScript error. Since jobs are loaded via AJAX, any JavaScript error can prevent the listings from displaying properly. If you’re not sure how to do that, you can follow this guide.
If you find any JavaScript errors, you will need to identify which plugin or theme is causing the error and fix it or disable the plugin/theme. You can try disabling all plugins and then enabling them one by one to determine which one is causing the issue.
Hope that’s all clear! Let me know what you find out, and we’ll take it from there if necessary.