TSM 3.7.4 on AIX 4.3.3

I have EXPIRE INVENTORY scheduled to run for 1.5 hours in the wee hours:
EXPIRE INVENTORY QUIET=YES DURATION=90


Sometimes EXPIRE INVENTORY runs OK.
Other times it starts up, examines/expires 200-300 objects, then shuts
itself down again in 2-3 minutes with the normal message of SUCCESS.

Now I know it should be expiring 100,000+ objects per day.
If I start it again manually, it takes off and runs as you would expect.

Does anyone else see this happen?
Any idea what causes the premature shutdown?