Hello Holger

Sorry for the inconvenience.

Can you please go to wpDataTables settings/Custom JS and CSS and add this in the Custom CSS section:

.wpdt-c .wpDataTables.wpDataTablesWrapper{
        position: initial !important;
    }
    .wpDataTables .dataTables_length select.selectpicker {
        display: inline-block !important;
        width: inherit;
        padding: 3px 24px 3px 8px !important;
    }
}

Please let me know if that resolves the issue.

I'm glad to hear that, Holger

If you have any further questions or issues, please feel free to open a new ticket, and we'll gladly help.

Hello again Holger

Can you check if the custom CSS is still in wpDataTables settings/Custom JS and CSS/Custom CSS field?

This is a bug, definitely, and this is a temporary solution until our developers include a fix in the plugin. If you still can't resolve the issue, please provide me a temporary WP-admin login for your site where this happens, so we could log in and take a look ‘from the inside’ as that’s the most efficient way to see and resolve the issue. We do not interfere with any data or anything else except for the plugin (in case that’s a production version of the site), and of course we do not provide login data to third party. 

You can write credentials here just check Private Reply so nobody can see them except us.