core: Generic Thermostat - graph not showing green fill after 0.96

Home Assistant release with the issue: 0.96.5

Last working Home Assistant release (if known): 0.95

Operating environment (Hass.io/Docker/Windows/etc.): Hass.io

Component/platform: Generic Thermostat

Description of problem: Almost the same as #25578, I think the problem is related to the HA thermostat component. And not the custom component of the other issue.

After 0.96 the climate history graph is not showing the status shaded part (if it’s cooling or not).

here is my entity status:

The history graph:

The history graph used to be something like this (the green part showing if it is actually cooling or not):

Problem-relevant configuration.yaml entries and (fill out even if it seems unimportant):

climate:
  - platform: generic_thermostat
    name: Ventilatie Receptie thermostaat
    heater: switch.ventilatie_receptie
    target_sensor: sensor.ventilatie_receptie_temperatuur_min
    ac_mode: true
    target_temp: 22
    initial_hvac_mode: "off"

Traceback (if applicable):

Additional information: It also happens in the Honeywell Thermostat integration, according to this topic.