Permission denied on NFS4 share with Ubuntu 14.04 client

[John Ratliff]

I setup an NFS4 server on Debian 9. I have no issues with permissions on 
other Debian clients I have tried (Jessie or Stretch Debian Versions).

However, I have 3 Ubuntu 14.04 servers, and I always get permission 
denied errors on these servers.

I am not using Kerberos. Just plain IP based authentication.

This is my entry on Ubuntu 14.04 fstab.

nfs:/x/share /mnt/nfs        nfs4    ro,proto=tcp,sec=sys 0 0

This is my exports file on Debian 9 server.

/export 
192.168.1.0/24(ro,fsid=0,no_subtree_check,sync)
/export/x/share 
192.168.1.0.0/24(ro,nohide,insecure,no_subtree_check,sec=sys)

Permissions on directory

/export/x/share 2750 (u+rwx g+rxs o-ALL)
Owner is root
Group is ssl-cert

The group ID on Ubuntu 14.04 is 999
The group ID on Debian 9 is 999

I made sure these were the same.

$ ls -l
total 4
drwxr-s--- 2 root ssl-cert 4096 Oct 13 14:37 nfs

$ cd nfs
-bash: cd: nfs: Permission denied

$ groups
jratliff adm sudo staff ssl-cert qmail

$ grep ssl-cert /etc/group
ssl-cert:x:999:jratliff

I've restarted every service I can think of on both the client and 
server. Then I rebooted them both, first the server then the client. No 
change.