Zwave mqtt value flashes unavailable for a short moment

Use ZwaveJS UI (2 x) and have a bit of strange behaviour. The MQTT readout of the sensors are there but constantly flash unavailable for a short moment. about one second interval. Barely visible.
It is consistant from both Zwave instances.
I have the ‘normal’ ZwaveJS enabled and no issue there. Sensors are stable.
My mqtt broker is on the same server and I see no issues with Zigbee2mqtt sensors or the Wifi to mqtt.

I have “retain” enabled and see no errors in the logs or history. It’s just a bit annoying on the dashboards.