You keep saying SMB is the issue, did you analyze the network traffic and find something? Did you debug the code? At the very least did you verify the same issue persists if you access the same share through a different protocol (maybe nfs)?
Just saying, the OP pointed at SMB too and it turnee out to be the wireless driver. All you really have found is that Kodi does not display everything in a given folder. Sure it could be SMB, but it could be something else entirely as well.