On website placed instructions how to usage PlantUML Server like proxy service. In example you use specific github reference (https://raw.github.com/plantuml/plantuml-server/master/src/main/webapp/resource/test2diagrams.txt) like a source of uml configuration. If you manually go by this reference you taking a response for github, which contain simple format text file. And when you try to transfer this file like source for proxy service all work fine.
Gitlab can provided the same simple format text file by this type references - https://gitlab.com/user-name/repository-name/raw/branch-name. (For example https://gitlab.com/MitLearnJSTest/wiki/raw/master/diagram.txt), user-name is optional in this case, because this repository is public.
But if you try to use this reference like source, for proxy service - you redirected to page with default example http://www.plantuml.com/plantuml/uml/SyfFKj2rKt3CoKnELR1Io4ZDoSa70000
Could you please help with this issue?