I would suggest you punch out the two dimpled crosspins, set into the lower edge of the receiver, one each, toward the front/rear of the side.
They are of slightly different size, so you know which home each belongs in.
Once they're "out", the trigger group (triggerguard housing with the firing & feed mechanism) should be able to be removed out of the bottom of the receiver with zero parts flying free.
Try cocking the hammer, and/or firing it via the trigger, manually while it's out of the receiver - and mayhaps you can see if there's any foreign matter in there, gumming up the works.
In any event, it's a good chance to flush out the firing group with a cleaner, and lightly re-lube the parts, before re-installing it back into the receiver.