There are times when I have had to "go the extra mile" to get a drawing cleaned up. I have a methodical sequence that I will go through when a drawing is being squirrely even after a -PURGE and AUDIT. My favorite is turn on, thaw, unlock all the layers, then use the standard Windows CTL-C to Copy everything to that nebulous clipboard that experience says is there, but never is seen. Then open a new drawing, and use the PASTE to ORIGINAL COORDINATES. Even after doing that, it is best to go through the -PURGE and AUDIT sequence. And don't forget Layout Tabs, that may be needed to CTL-C and PASTE into the new drawing as well.
But then there have been other times where even the CTL-C and PASTE sequence leaves garbage in the drawing...or more accurately, copies the garbage over. That would then lead me to the next option, which is to run DXFOUT. This often times will expose multiple hidden blocks that once revealed, can now be PURGED out to the drawing. Remember then to SaveAs to a DWG. Another trick on getting the Layout Tabs, if needed, is to use the Design Center to pull them over.
Another sequence I have had success with to restore a drawing to it's functioning glory, is to INSERT it into a new drawing with the Explode option selected. But even stranger, I have had drawings that would not even open in AutoCAD nor INSERT, but would be visible as an XRef. So, after XRef-ing in a drawing, then BIND as an INSERT, then explode and PURGE and the drawing was then fully functional once again.