Found a work around. Instead of configuring the things in PaperUI, I configure the MQTT Gateway and the sensor through the openHab things file. I followed the example that @dakipro wrote in the openHab controller main Web page (https://www.mysensors.org/controller/openhab). Thanks @dakipro.
In the relay actuator example the methods saveState() and loadState() are used. The current status of the pin (RELAY_ON or RELAY_OFF) is stored in the EEPROM with every change and restored after a restart of the node.
The node will return to the last known state after a restart.
BUT: while restarting the state of the pin may change (from on to off to on again while booting up). In case you want the relays to stay activated while booting up you may use an external pull up.
OK got it !!! It was a combination of more failures - with the main one not having read the name of the status message carefully enough : ItemStateChanged(!!!)Event. So as long as battery level is the same ...