Template Sensor zeigt nur "unbekannt"

[nichname]

folgendes Template zeigt nur "unbekannt" an.
state: Teil funktioniert im Template-Editot einwandfrei. Woran kann es liegen?

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# Zeit seit Sonnenaufgang
  - name: "Time Since Sunrise"
    unique_id: "time_since_sunrise"
    state: |
      {% if states('sun.sun') not in ['unknown', 'unavailable'] %}
        {% set sunrise = as_timestamp(state_attr('sun.sun', 'next_rising')) %}
        {% set now = as_timestamp(now()) %}
        {% set last_sunrise = sunrise - 86400 if sunrise > now else as_timestamp(state_attr('sun.sun', 'last_rising')) %}
        {% set diff = now - last_sunrise %}
        {% if diff > 0 %}
          {{ diff | timestamp_custom('%H:%M:%S', false) }}
        {% else %}
          00:00:00
        {% endif %}
      {% else %}
        unknown
      {% endif %}
    availability: >
      {{ states('sun.sun') not in ['unknown', 'unavailable'] }}
    icon: mdi:weather-sunset-up
    unit_of_measurement: "hh:mm:ss"