I just checked to protocoll file to add detail. You can see that the plugin generates the issue:
2020-01-15 14:23:49 Access 217.80.245.7 200 GET /wordpress/wp-admin/admin.php?page=internetmarke_dp_shop HTTP/1.0
2020-01-15 14:23:52 Error 217.80.245.7 404 GET /wp-admin/images/spinner.gif HTTP/1.0
And with the 404 error my ISP blocks my IP and I can no longer access my WP site. Now that is very bothersome!