Yes NFS is an option, but I wanted to know why SMB wasn't working
I've discovered on kodi.tv that there is a SMB performance bug in the 4.19 kernel. You need to /flash/extlinux.conf and add pci=nomsi
the /flash filesystem is read-only so you'll need to remount it: mount -o remount,rw /flash
Hope this helps anyone havin SMB performance issues, it worked for me.