Interior Ceiling Structural Problem
This could be some serious structural damage and
should be addressed as soon as possible. When ever you run across a
situation like this while doing your home inspection, you should use
caution, walking around in the attic.
There could be more damage, creating a safety problem, walking on the ceiling joist or attic access area.
If this area is accessible, above the drywall, there's a good chance you will find some sort of problem here. The problem could be termite damage, wood rot or a structural framing issue.
The way that the interior ceiling has caved in around the post is a clear sign, that there has been movement in the ceiling framing.
It's hard to tell what caused this damage, from looking at it from below. You will have a better chance at discovering the problem if you have access above.
If there is no access above, someone will have to remove a section of the ceiling drywall, to examine the area and determined what the problem actually is.