Statistics on Reimann Integral

I’m using Reimann Integrals to sum a few sensors, eg my MVHR airflows and I was hoping to be able to display yesterday’s total airflow using the Statistics card. I get just a question mark displayed.
As an example:
In configuration.yaml

  - platform: integration
    source: sensor.mvhr_exhaust_airflow
    name: mvhr_exhaust_integral
    unit_time: h
    unique_id: mvhr_exhaust_integral

Which does indeed add up the cumulative airflow. However this lovelace card does not display yesterday’s total and clicking on it shows the current total but under History: “no statistics found”:

type: grid
title: Averages yesterday
  - type: statistic
        period: day
        offset: -1
    stat_type: change
    entity: sensor.mvhr_exhaust_integral
    name: Exhaust

Any idea what’s going on here?