Interesting problem and as usual with very little info.
Fortunately there is a clue in the output:
From 192.168.131.254: icmp_seq=1 Redirect Host(New nexthop: 10.1.2.20)
The "Redirect Host" tells me the VPN router "thinks" the destination is somehow directly connected.
From experience I know the Pi does not handle ICMP redirects like your windows machine does but this is not as it should be.
It does explain why your windows machine is working ok.
The suggested fix (to add a static route for the 10.x network) may not solve the problem but its still worth trying.
Otherwise you need to check the configuration of your VPN connection.
This could introduce a performance improvement for the windows box as well when the redirects are no longer sent.