Also possible that the screw under the top lever was not tightened enough and so trigger plate is not hitting the sear/s hard enough. That screw and ever screw slot should be orientated to face the length of the barrels (except the top lever screw that rotates when the barrels are opened)
The screw under the top lever is tapered like the top tang and that is what I would look at to see if it is correct, if not one more full turn.
Also with the left lock off you can see if the trigger plate is going far enough to hit it solidly.