As they exited the plane this jumper’s deployment bag came out of their container and gave them a horseshoe malfunction. They realized their pilot chute was still in the BOC and deployed it in an attempt to remedy the situation. Unfortunately, the pilot chute failed to extract the main, resulting in a SECOND malfunction! This time the jumper was faced with a bag lock. They cutaway their main, regained stability and deployed their reserve.
This malfunction occurred because the jumper exited the aircraft in a manner which scraped the back of their container across the side of the aircraft. This may have dislodged the pin, or it could have exposed bridle which then caught air and dislodged the pin. Either way, the deployment bag left the container with the pilot chute still inside the BOC.
In this scenario, the bag lock was almost certainly the result of the horseshoe. When the jumper deployed their pilot chute it got caught up in their lines and almost certainly prevented the bridle from being able to extract the main.
The easiest way for this jumper to have prevented this malfunction would have been for them to make sure to rotate their container away from the side of the plane when exiting the aircraft. Sometimes jumpers are rushing to get out and they forget this basic rule!
This bag lock was likely due to the horseshoe. So, preventing the horseshoe would have probably prevented the bag lock! It should be noted, however, that bag locks occur for many other reasons. Line stows that were left too long can lock one another off, a stow can get pulled into a grommet, a pilot chute can be in need of replacement, etc. A majority of bag locks can be easily prevented. Proper packing is the first step: ensure your line stows are the proper length, double-stow your rubber bands, don't leave too much excess, etc. Additionally, ensuring that your gear is in good working order plays a role because a worn-out pilot chute may not have enough drag to provide for the proper extraction of a main.
In this video the jumper did not have an RSL or a Skyhook and, after cutting away, took a significant delay before pulling their reserve handle. In this case the individual had plenty of altitude to enjoy a short belly jump. However, there have been incidents where a jumper took the time to get stable in an attempt to ensure a clean reserve deployment and their delay resulted in serious injuries and death because they didn’t realize how low they were. Typically, if you’re going to cutaway you should go to your reserve immediately.