I have a write up here with a number of other CLI tricks:
https://whyistheinternetbroken.wordpress.com/2015/02/16/techbecome-a-clustered-data-ontap-cli-ninja/
It's from 2015, but much of it still applies.
Connected clients will only show active mounts. If a client has not been used for a while (meaning it's mounted but never is accessed) then it won't show up in that list.
For example, this client has a mount to "home", but only populates the cache when I cd or run ls to it.
demo:/home on /mnt/home type nfs4 (rw,relatime,vers=4.1,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=10.x.x.x,local_lock=none,addr=10.x.x.y)
ontap9-tme-8040::*> nfs connected-clients show -node ontap9-tme-8040-0* -client-ip 10.x.x.x -volume home
There are no entries matching your query.
# cd /mnt/home
# pwd
/mnt/home
ontap9-tme-8040::*> nfs connected-clients show -node ontap9-tme-8040-0* -client-ip 10.x.x.x -volume home
Node: ontap9-tme-8040-02
Vserver: DEMO
Data-Ip: 10.x.x.y
Client-Ip Volume-Name Protocol Idle-Time Local-Reqs Remote-Reqs
--------------- ---------------- -------- ------------- ---------- -----------
10.x.x.x home nfs4.1 19s 2 0