samba - Nov 2016 - remote browse sync triggers error Packet send failed

Hello,

I need to use WINS browsing to allow Mac computers to list Windows served
printers.
Mac clients and Windows print server (Windows 2012R2) are on separate subnets:
- Mac clients on 10.1.0.0/16 subnet
- print server on 10.10.0.0/16 subnet

A Samba server (10.1.10.24) is a master browser on subnet 10.1 and another Samba
server (10.10.31.73) is a master browser on subnet 10.10
each server has only one network interface on its subnet.
So referring to https://www.samba.org/samba/docs/using_samba/ch07.html I thought
the remote browse sync would allow any SMB Client (including Mac) with
10.1.10.24 as WINS server to also list the browse list from subnet 10.10 ?

smb.conf WINS config on 10.1.10.24:
wins support = yes
dns proxy = yes
local master = yes
 os level = 255
preferred master = yes
remote browse sync = 10.10.31.73

smb.conf WINS config on 10.10.31.73:
wins support = yes
name resolve order = wins
dns proxy = yes
local master = yes
os level = 255
preferred master = yes

Something does not work as expected because browse list from subnet 10.10 is not
available to clients on subnet 10.1
nmbd log file on 10.1.10.24 shows error: Packet send failed to 10.10.31.73(138)
ERRNO=Invalid argument

firewall between 10.1.10.24 and 10.10.31.73 lets every network flow both
directions.
A network capture shows no communication from 10.1.10.24 to 10.10.31.73

Any idea about what goes wrong here ?

Thank you
Alban