Connecting SL 4 with border router

In your instructions about connecting the smartlock with Homeassistant over matter you write that there may be only one border router in Homeassistant.
This is a sonoff dongle in my situation and I connected the smartlock successfully. But as soon as I plug in my Amazon echo which have a border router also the connection stops working. But I can’t disable that. Is there any way that I can use the echo parallel?

Which connection stops: “remote access” or Matter or both?

The matter connection between the smartlock and the border router. But in the meantime it is stable. It looks like it needed some time to reorganise the network.