I have also tried
//192.168.1.139/osmc/roms /home/osmc/RetroPie/roms/ cifs auto,x-systemd.automount,username=guestread,password=XXX,_netdev,uid=1000,iocharset=utf8,sec=ntlm 0 0
And
//192.168.1.139/osmc/roms /home/osmc/RetroPie/roms/ cifs auto,x-systemd.automount,cache=none,rsize=130048,wsize=57344,users,username=guestread,password=XXX,_netdev,uid=1000,iocharset=utf8,sec=ntlm 0 0
to no avail…