actually you can see in the the log ubuntu tried v4 and fails, then tries v3 and still fails
manually specify vers does not change the behavior
I tried vers=3 and vers=2
but another interesting observation
when I boot SMP nfs-server appears fine
after I attempt to mount from ubuntu
nfs on webend goes red
and pidof nsfd does not return any result and nothing in process list
and if I retry test from ubuntu
showmount and rpcinfo shows that the nfs server has indeed stopped
then if I try to restart the nfs server on SMP, output looks fine
but on ubuntu side showmount starts working again
rpcinfo -p 192.168.1.25 is working again
rpcinfo -u 192.168.1.25 nfs shows that this was not correctly restarted "not available"
rpcinfo -u 192.168.1.25 mountd is working again
on smp side pidof nsfd indeed does not return any result, so nfsd service can not be restarted for some reason