Eth one way only

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
and Gateway
All settings confirmed with lsconfig.

Desktop Debian 10 on
BBB Debian Stretch on
Laptop Mint 19 on

Testing the connections with Ping:
From Desktop OK (Router)
with Debian 10 OK (self) BBB Unreachable OK

From Laptop OK (Router)
with Mint 19 OK OK OK (self)

From BBB OK (Router)
with Debian 9 OK OK (self) 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.