In the past I have read about other people having this issue but have never experienced it myself until I setup a new server.
This happens with mhddfs or mergerfs and both are fuse based so I suspect this might have something to do with it.
I can add the shared directory over NFS but only the the first directory and all files show as zero bytes.
subdirectories are not able to be entered into.
username, GID & UID (1000) are the same on both server and client.
OpenElec does not seem to suffer from this setup but standard linux & android based kodi builds do.
I changed all permissions on the folders to drwxrwxrwx
I seem to remember a setting in the exports that needed to be set but it no longer works, noreaddirplus
If I mount the NFS share on the client with fstab or manually there is no problem.
Debug here http://pastebin.com/MAG6PnLe
/etc/exports
/media/POOL 192.168.20.0/24(fsid=123,rw,no_subtree_check,insecure,all_squash)