This video does not show the common gremlin. The common gremlin is a timing issue where the striker follows the bolt into battery, so when the trigger is pulled nothing happens -- the striker is already forward. Tabbing the carrier is the simplest and most robust fix.
The video shows another problem where the sear or safety walks laterally and the two get aligned and make contact, so that when the trigger is pulled, the disconnector doesn't release the sear and nothing happens. The gun is in effect, on "safe". The striker, however, is still cocked and ready to go. If the sear or safety pin is tapped back into position, then the trigger will be able to release the striker. This problem is less common than the gremlin. The fix in the video is valid, but another solution is to remove the safety mechanism and file the groove a little wider so that if either the sear or the safety walk laterally, the wider groove will prevent contact between the two and keep the trigger in action. In the video you can see that groove when the sear is removed.