If I’m not mistaken, that is a sear lock. The sear lock knife is supposed to be operable with a single hand (usually right hand unless the knife is custom-made for lefties). Lefties using these knives will need a strong index finger instead of thumb to disengage the sear.

If it CAN be closed, and several times already, I would guess that the knife works just fine. From here I can’t tell if it’s user error or faulty mechanism at play.

Perhaps you might want to try opening the knife realllly slowwwly up to the point when the sear “click” into locking position while you eyeball the inside of the knife to see how it works, or to check if there is anything weird blocking the springy bar from being pressed open.