Yes, Fabian, it seems to be something other than the properties.schema. I successfully uploaded it in my local installation of the authoring tool. I took the zip file you provided, extracted it, replaced the properties.schema with the version you had provided but amended it as I had recommended (deleted "editorOnly" from "characterId), zipped it again, and uploaded through the Plugin Manager. I did not get the "failed to parse" error.

Once in the component editor, however, no fields were available for configuration. So, expect that you still have some issues to confront once you get passed the "failed to parse" error.