Wish you had taken a third picture of the forward parts.
Just a guess, but
Bet the ejector rod wasn't screwed all the way on, was hitting the barrel shroud, and wouldn't allow the cylinder to close.
Hard to imagine that whoever worked on it the first time didn't see that.
If so, it's no big deal and a common occurrence.
Just a revolver thing.
Walt Kelly, alias Pogo, sez:
“Don't take life so serious, son, it ain't nohow permanent.”