During dry fire practice with my left hand I tilt the gun inward so my dominant right eye gets a better front sight picture. For idpa and uspsa needs it really works on all my guns.

I don't know if it was my left hand fatiguing or what, but the trigger would not go all the way back sometimes if I had the gun held way over to the right.

Is this the transfer bar moving and now allowing the hammer to go back and forward. A safety measure.

Addendum: never mind. It was finger fatigue. I just shot the 625 completely flat (the gun, not me) and it went off each time. This with refreshed left trigger finger.

It could also be a problem with "sing", it doesn't always happen every time but if you're pulling the trigger in just the right way for it to happen, if there's trigger "slop" side to side it can bind the gun up when the hand doesn't contact the ratchet teeth correctly due to a different trigger pull.

Some people have said they have old, worn revolvers that time perfectly in DA right handed, but carry up "short" when they shoot left handed, or vice versa.