@Christoph-Hart I'm also still encountering this issue.
I've also tried all kinds of formats
"{PROJECT_FOLDER}/Scripts/test.js"
"{PROJECT_FOLDER}/Scripts/ScriptProcessors/test.js"
"{PROJECT_FOLDER}/test.js"
I also get onControl cannot be parsed.
My test.js is a file I saved after adding a blank script processor to my container.
1:
"Right-click/connect to external script": Works!
"Rick-click/reload connected script": Works!
2:
Adding script via Builder.connecttoScript: On Control cannot be parsed.
"Rick-click/reload connected script": Does not work "because connected script is not a valid HISE script. OnControl( cannot be parsed"