When using a custom configFile, the CKEditor does not find it and uses a fallback CKEditor

Steps to reproduce:

• Rich text definition with a custom configFile:

  form:
    properties:
      richText:
        label: Text editor
        $type: richTextField
        height: 500
        tables: true
        source: true
        configJsFile: /.resources/ckeditor/ppconfig.js
  

When opening the richTextField with CKEditor, a warning is thrown:

15-Oct-2020 16:09:03.517 WARNING [http-nio-8080-exec-3] com.vaadin.server.communication.PublishedFileHandler.handleRequest vaadin-save-plugin.js published by info.magnolia.ui.vaadin.ckeditor.MagnoliaCKEditorTextField not found. Verify that the file info/magnolia/ui/vaadin/ckeditor/vaadin-save-plugin.js is available on the classpath.

The opened CKEditor is not the one we were trying to use, but a fallback CKEditor.

Even when using a simple richText field with no custom configFile, we get the warning but the Magnolia CKEditor is used.
This is the definition I used:

form:
  properties:
    text:
      label: Text editor
      $type: richTextField
      height: 500
      tables: true
      source: true

Outcome:
Issue wasn't reproducible, however, a glitch was found in the legacy pages app where drop down menus in a custom config would be hidden behind Vaadin's modal dialog. This has been fixed in the scope of this ticket.