MQTT Sensor doesn't get second part of json string

I have a sensor out in the garden that sends the following over MQTT:

{"ds18b20_temperature": 16.5, "garden_cpu_temp": 32.172}

I have this in my config.yaml:

mqtt:
  sensor:
    - name: "Garden Temperature"
      state_topic: "garden/temperature"
      suggested_display_precision: 1
      unit_of_measurement: "°C"
      value_template: "{{ value_json.ds18b20_temperature }}"
    - name: "Garden CPU Temperature"
      state_topic: "garden/temperature"
      suggested_display_precision: 1
      unit_of_measurement: "°C"
      value_template: "{{ value_json.garden_cpu_temp }}"

BUT I am only getting the garden temperature. The garden CPU sensor returns “Unknown” on the dashboard, and I can’t work out what I’ve missed

I took out the following line and it worked!

      suggested_display_precision: 1