This isn't the place to define a share. As it is now, the "include = /etc/samba/smb-shares.conf" is being added to the [system] share because it is right after the smb-extra.conf include in smb.conf and the scope is still [system] when it returns to smb.conf and not [global]. The smb-extra.conf settings are global.
I don't know your disk and shares configuration, but set up a [system] share on your cache disk? Hopefully your cache is not on the array.
There is no need to add it manually. The include is in smb.conf. Again, don't depend on testparm to show the includes properly.