I think it may be unlocking micro-seconds after the discharge.
You can actually verify if the above statement is correct by trapping the slide when the gun is fired. In one of the SD classes I had, we were taught about grabbing the gun forward of the trigger and holding it tightly such that once the gun was fired (and hopefully it wasn't pointed at you), that the trapped slide would result in no spent case ejection and no recocking of the gun.
It takes a firm grip to do this and if you do it bare handed and didn't have the slide fully trapped, the front recoiling across your palm or fingers isn't pleasant. You can reduce that risk by wearing a decent set of leather gloves. Also, even if you fully trap the slide barehanded, there can be a little sting to the palm and fingers, but nothing significant.
So if you fully trap the slide and fire the gun, you can then manually cycle the action and inspect your spent case. If it still looks the same, then the issue isn't unlocking quickly. If the brass looks good, then apparently it is unlocking quickly.