KeyError: 'slow_route'

KeyError: 'slow_route'
  File "pyramid/router.py", line 270, in __call__
    response = self.execution_policy(environ, self)
  File "pyramid/router.py", line 279, in default_execution_policy
    return request.invoke_exception_view(reraise=True)
  File "pyramid/view.py", line 768, in invoke_exception_view
    reraise_(*exc_info)
  File "pyramid/compat.py", line 179, in reraise
    raise value
  File "pyramid/router.py", line 277, in default_execution_policy
    return router.invoke_request(request)
  File "pyramid/router.py", line 249, in invoke_request
    response = handle_request(request)
  File "cubicweb_francearchives/pviews/tweens.py", line 56, in sanitize_parameters_tween
    return handler(request)
  File "cubicweb_francearchives/pviews/tweens.py", line 103, in script_name_factory
    return handler(request)
  File "cubicweb_francearchives/pviews/tweens.py", line 86, in https_tween
    return handler(request)
  File "cubicweb_francearchives/pviews/tweens.py", line 74, in langprefix_tween
    response = handler(request)
  File "cubicweb_prometheus/views.py", line 137, in tween
    PD_METRICS["slow_route"].labels(route_name).inc()