Openhab sends "null" Payload - Zigbee2mqtt & Mosquitto Broker - Heating Setpoint as Dimmer


after sometime my Heating Setpoint Dimmer doesnt work anymore. At first Zigbee2mqtt seems to gets everytime the same value, doesnt matter what choose at the slider. because of that, i tried to recreate the whole Thing, Equipment, Point and Item severals times, and after that, Zigbee2mqtt seems the get an empty payload from Openhab:


Debug 2022-09-12 11:49:26Received MQTT message on 'zigbee2mqtt/TRV_KZ/set' with data ''
Error 2022-09-12 11:49:26Invalid message 'null', skipping...

Openhab events.log:

2022-09-12 11:49:23.114 [INFO ] [openhab.event.ItemCommandEvent      ] - Item 'Thermostat1_AktuelleSolltemperatur' received command 19
2022-09-12 11:49:23.117 [INFO ] [penhab.event.ItemStatePredictedEvent] - Item 'Thermostat1_AktuelleSolltemperatur' predicted to become 19
2022-09-12 11:49:23.126 [INFO ] [openhab.event.ItemStateChangedEvent ] - Item 'Thermostat1_AktuelleSolltemperatur' changed from 15 to 19


UID: mqtt:topic:MOSQUITTO:TRV_1
label: Thermostat 1
thingTypeUID: mqtt:topic
configuration: {}
bridgeUID: mqtt:broker:MOSQUITTO
location: Kinderzimmer
  - id: CH_TRV_1_heatingsetpoint
    channelTypeUID: mqtt:number
    label: Aktuelle Solltemperatur
    description: ""
      unit: °C
      min: 5
      formatBeforePublish: '{"current_heating_setpoint": "%s"}'
      max: 30
      commandTopic: zigbee2mqtt/TRV_KZ/set
      stateTopic: zigbee2mqtt/TRV_KZ
      transformationPattern: JSONPATH:$.current_heating_setpoint

Item config (Modell)

Does anybody know what iam doing wrong? Other Commanding things seems to work fine (switches for away_mode or Windowdetection).

Device: Saswell SEA801-Zigbee/SEA802-Zigbee control via MQTT | Zigbee2MQTT

Kind Regards