Hello,
Please note that BSP modifications are beyond the free support scope. The reason is that it is hard for us to find the root cause of these kind of problems if we cannot reproduce the issue on our own boards.
In your case it looks like you have made changes in RTCS transport layer (TCP/UDP), however, there could be something else that must be modified in lower layers that is causing the ARP mesagges to be received on your PC application, so basically, as ARP is a Data Link layer protocol you will need to debug the stack on lower layers.
Regards,
Isaac