Instructions for Apache HTTP Server
Some Confluence installations are using Apache HTTP Server as a proxy between the browser and the Confluence server.
Sometimes Apache server is not configured to properly serve SVG files. As a result, SVG icons in the draw.io diagram editor will look like on the screenshot below.
In that case, edit the server's configuration file and add the AddType directive to allow for SVG files to be served with a proper MIME type. Below is the snippet of the example http.conf file.
AddType directive needs to be added within the <IfModule mime_module> block.
Save the changes and restart the Apache HTTP server. To confirm the SVGs are now served properly, re-open the draw.io editor.