Troubles with various ZWAVE devices

I am using a variety of Z-Wave devices. So far, so well. Recently I am experiencing troubles with the devices, which are not zertified according to ZWave Plus, namely a PHI_PAN06 “Relay Insert 2 * 1.5 kW” and a ZME_06433 “Dimmer”.Both devices have worked before to my satisfaction. I have recently experienced, that the communication to the controller keeps breaking down more and more often. Commands sent from OpenHAB are not beeing executed. I do not see any error messages in the log.

The strange thing is, the relay still reacts on commands from a scene controller and the dimmer still executes button presses on the device itself correctly. So, both devices seem to work at least to some extend. While the dimmer is shown as “ONLINE” in the Configuration/Things view, the relay shows as “OFFLINE - COMMUNICATION_ERROR / Node is not communicating with the controller”.

Any help on this would be greatly appreciated.