Unable to ssh or login to AIX server

We are having occasional problems accessing some AIX servers. When this happens we cannot ssh to the server in question or login via HMC console terminal window. We can ssh some commands to the server and get responses but other commands just hang, ssh serverA date returns the date, ssh serverA df -g hangs. This has happened on as least 3 different VLPARS all at AIX 7100-02-03-1334. Any thoughts or suggestions would be welcome, we also have an active PMR open with IBM support but nothing concrete from that yet.

Thanks Kierong