Unable to add a Activity from the existing catalog

I might be facing this issue, and can maybe provide more info:

The error in JS is truly a 404 exception that is caught by the JS main.bundle.js. This is triggered due to the checkbox of selecting the existing activity in the sidebar using url: "https://DOMAIN/module/19/add-activity/57/group/DOMAIN,opigno_module,19,i..."

As you can see, this is not a proper url since this routing should be:

opigno_module.manager.add_module_activity:
  path: '/module/{opigno_module}/add-activity/{opigno_activity}/group/{group}'

This "group" variable is then not properly handled by the JS app, since I would expect a numeric ID to be present on the group. I would assume the error is around this file:
* "opigno_group_manager/ng/src/app/activities/activities.service.ts"

Probably here, or whoever is passing that "group" variable:

  addActivity(moduleId, activityId): Observable<any> {
    const group = this.getParams(window.location.href, 'group');
    return this.http
      .get(this.apiBaseUrl + this.appService.replaceUrlParams(this.addActivityUrl, { '%opigno_module': moduleId, '%opigno_activity': activityId, '%group_id': group }))
      .map(response => response.json() as any);
  }

But this is all guessing, since I'm not sure how to debug the JS app easily.