Shelly TRV setting itselfs to 20°C

Hi, I am using a schedy schedule to controll my radiators with ShellyTRVs.
The trvs are connected via coiot, not mqtt.

For some reason (at least) one of the trvs keeps setting itselfs to 20°C after returning from an open-window period

2023-01-09 08:25:56.663671 INFO schedy_heating: --> Attribute 'state' of 'binary_sensor.zsens_sz_fenster_ias_zone_delayed' changed from 'on' to 'off', reevaluating <Room R:Schlafzimmer>.
2023-01-09 08:25:58.136942 INFO schedy_heating: --- [R:Schlafzimmer] Restoring overlaid value 14.0??.
2023-01-09 08:25:58.164268 INFO schedy_heating: <-- [R:Schlafzimmer] Value set to 14.0??.  [manual]
2023-01-09 08:25:59.623020 INFO schedy_heating: --> [R:Schlafzimmer] [A:climate.shellytrv_schlafzimmer] Received value of 14.0??.
2023-01-09 08:26:00.603744 INFO schedy_heating: --> [R:Schlafzimmer] [A:climate.shellytrv_schlafzimmer] Received value of 20.0??.
2023-01-09 08:26:00.614123 INFO schedy_heating: --- [R:Schlafzimmer] Re-applying the schedule not before 09:26:00 (in 1:00:00).
2023-01-09 08:26:05.545848 INFO schedy_heating: --> [R:Schlafzimmer] [A:climate.shellytrv_schlafzimmer] Received value of 14.0??.

Unfortunately the reset (last line) to the requested temperature does not always happen within 5 seconds.
Any idea what is happening here?

The device log shows the trv becoming unavalable intermedately

(roughly translated)

08:27:05 - changes to heating on
08:27:05 - no longer avalable
08:25:59 - changes to heating on, triggered by service climate.set_temperature
The schedy schedule looks like this
schedy_heating:
  module: hass_apps_loader
  class: SchedyApp

  actor_type: thermostat

  expression_environment: |
    def heating_mode():
        return state("input_select.heating_mode")
    def is_occupied():
        return is_on("binary_sensor.wohnung_bewohnt")
    def is_workday():
        return is_on("binary_sensor.workday_sensor")

  watched_entities:
    - input_select.heating_mode
    - binary_sensor.wohnung_bewohnt
    - binary_sensor.workday_sensor

  rooms:

    Schlafzimmer:
      watched_entities:
        - binary_sensor.zsens_sz_fenster_ias_zone_delayed
      rescheduling_delay: 60
      actors:
        climate.shellytrv_schlafzimmer:
      schedule:
        - name: "Turn off in summer-mode"
          x:    "OFF if heating_mode() == 'Sommer' else Next()"
        - name: "Turn off when window open"
          x:    "Mark(OFF, Mark.OVERLAY) if is_on('binary_sensor.zsens_sz_fenster_ias_zone_delayed') else Next()"
        - name: "Turn on during daytime in homeoffice mode"
          v: 19
          rules:
            - x: "Next() if heating_mode() == 'Homeoffice' and is_workday() else Break()"
            - { start: "09:00", end: "17:00" }
        - name: "Set to 14 in all other situations"
          v: 14