Dead 'undead' nodes


I completly reinstalled my Home Assistant including the Z-Wave and all it’s devices.
The problem is, and was before reinstalling, that my battery nodes show “dead” in the Network Graph.
But they do all work, can ping, give temperature etc. I do not understand why they show “Dead/Grey”.

In the very beginning (year ago or so) this did never happen.
If they after some days get “connected” in the Graph, than after a restart they all “Dead” again.