Hatman's KWC 1911 - Ongoing issue

[ATF-Hatman]

Now I wonder if I'm simply flogging a dead horse.

When the slide is disengaged from it’s locked position, the barrel on occasion will fall all the way out.

I have disassembled the gun to the limits I am comfortable with at this point but cannot access where the brass barrel slides into the receiver to check it’s seating. (drawing of the barrel is also shown)
Anyone have any ideas as to what it could be that’s wrong?