Homematic Binding loses Illumination state

i used the channel of the hmip-spi of the current illumination to decide if a light should be turned on or not. Unfortunately openhab loses the state of homematic item. it shows NULL altough in raspberrymatic it shows a number for the illumination.
any idea how this can happen ?

Please check the log files openhab.log and events.log. Maybe there is an error message in openhab.log that can give a hint. Does events.log shows information about received values?

In order to give you a better advice, I would need more information:

  • openHAB version
  • How did you define the item? Main UI or text file.