The most likely cause is that the LAN subnet where the Network Interfaces are and the LAN subnet where the NetworkRepeater is, are connected so that UDP messages can pass between the nets, or that the NetworkRepeater and the Network Interfaces are placed in the same subnet. The NetworkRepeater then gets the same Mimer messages from the Network Interface that it is expected to be sending out, and this causes an error.
The NetworkRepeater shall be connected in the same LAN subnet as the operator PC´s. And the Network Interfaces shall be connected to the NetworkRepeater using TCP via at least one router over WAN or the Internet from another LAN subnet.