ping isnt working

I have two ConnectCore boards that I have connected to each other via wifi-direct as it says here: under Wi-Fi extender with BATMAN layer 2 protocol
and here and it works OK.

Now I have those two boards that connected (wi-fi) to each other and talk to each other, and I have my PC that connect to one of the boards with cable (via hub)

The ping from the PC to the boards is working, but the ping from the boards to the PC isn’t.
(what bothers me is the board that is connected to the PC with cable)

Any hint ?

Thanks a lot