TP-Link Deco M5, no internet no local connection thru ethernet port

Please Help,

I have many TP-link Deco M5 mesh network units in different locations and I have been very satisfied with this system. In two locations I run HA in that environment

However I found one very bad feature in these for home assistant. The problem is when you lose your internet connection. I had my doubts here - there were signs that this was not probably working. I started to check that today. This is what I found:

When I pull my ethernet cable out from my main Deco unit (Bridget thru the modem), basically all the mesh is still working “locally”. I can see all the devices connected to the mesh and I can connect them and ping is working - except one:

RPI handling the automation is connected to the main Deco with ethernet cable on the other ethernet port (there are two of them per unit), once the internet is lost the other ethernet port loses the connection to the mesh also, no ping no active device in the mesh. No working automation either?

In the other Deco units in the same network (not the main Deco) all the ethernet ports still work and the devices are connected and you can ping them.

I have Deconz Raspbee shield (no wlan?) ->solution is not using wlan here with RPI, it needs to be a cable and it needs to connect the main Deco.

Any idea is my main Deco OK or is it not working as it should?

I will highly appreciate all the answers - please help.