If you are talking about the pin that fits in the side, It is a retaining pin, kept in place under pressure (cocked). Usually happens when taking out the decocked trigger for cleaning and it falls on the floor.
How did you find it?
Exactly as you described. But prior to taking out the trigger group to see what was malfunctioning the trigger stopped working in the middle of a round of 5 stand.
It must have come loose and come out or partially out before I pulled out the trigger. Thinking of putting some locktite on it. Sound ok?