Xiaomi Mi Smart Home Binding: Bridge goes offline in OH3 M2

Back again with some news and findings.

In the documentation there is following sentences:

At least every 10 seconds you should see a message coming in from the gateway which looks like {"cmd":"heartbeat","model":"gateway","sid":"xxx",“short_id”:“0”,“token”:“xxx”,“data”:"{"ip":"xxx\"}"}

I have tried with OP2.5 and OP3.1.0

On the OP2.5 every 10 seconds I got this line.
On OP3 it comes up only, if I activate the Xiaomi Bridge.

So I believe something with the Server is maybe not working. wrong IP Settings Multicast ect.
Do anyone have an idea. I think there is no heatbeat, and after 5min it will go offline.
But I do not know why the Bridge is not sending the heatbeat to OP3

I already read the link - 87211
But I do not see any helpful ideas