Eth one way only

[jwvande...@gmail.com]

Hi All

I have the following connected  on Ethernet to a Netgear router.
Wifi disabled on all, no Internet connection.
Using ConnMan the IP's are set manually with NetMask 255.255.255.0
and Gateway 192.168.0.1
All settings confirmed with lsconfig.

Desktop Debian 10   on 192.168.0.2
BBB Debian Stretch on 192.168.0.4
Laptop Mint 19         on 192.168.0.6

Testing the connections with Ping:
From Desktop    192.168.0.1 OK (Router)
with Debian 10    192.168.0.2 OK (self)
                         192.168.0.4 BBB Unreachable
                         192.168.0.6 OK
               
From Laptop     192.168.0.1 OK (Router)
with Mint 19      192.168.0.2 OK
                       192.168.0.4 OK
                       192.168.0.6 OK (self)
               
From BBB        192.168.0.1 OK (Router)
with Debian 9    192.168.0.2 OK
                        192.168.0.4 OK (self)
                        192.168.0.6 OK

I have tried so many thing that I have lost track.
The idea is to do the development on the Desktop, send the files to BBB and compile.
So from the above it seems that Debian 10 can ping everything except the BBB, yet responds
to pings from the BBB and others.

Would love to hear some suggestions on how to solve this problem.

Regards