Try using startmaxl instead of essmsh.
startmaxl can be found under <MIDDEWARE_HOME>\user_projects\epmsystem1\EssbaseServer\essbaseserver1\bin on Essbase server.
I dont know how to append above path in Unix system variables. but should be similar to what we do in Windows i.e. adding path to system variable PATH
or From command line, go to above path & run startmaxl.
See if this helps to narrow down the issue.
I don't mean to be disagreeable, however we have been running this release for over a year without an issue. I'm thinking this AIX patch is affecting the system unexpectedly or the admins did something different on this server compared to the others. Last week everything was ok, then after the patch it breaks. I did test on our development server and was able to reproduce one time. restarting essbase services and reran several times to see if it would fail again and it did not fail to run.
We have incorrporated the startmaxl script settings with our environment so we do not have to run it that way due to extensive automation scripts would have to change.