Active Siteimprove Plugin behind firewall causing no page editing possible

We activated the siteimprove plugin, which is working fine on an local magnolia author instance. Activating it on a development environment behind a firewall, leads to a 504 Bad Gateway Error and none working ui widget for editing pages. You kann not simply open a page to edit content anymore.  
See screenshot and attached log file.

We would suggest, in an error case, simply the included plugin does not work, without causing other side effects.