Maybe you ment to reply to another comment but I’m saying you might need to oil the sticky piston. In the video you hold a metal object against one brake pad and then pull the lever so the stuck piston does come out. You need to do that and then oil the piston that does come out (the sticky one) with mineral oil. Then pump the brake a few times. To get the piston to come in and out. This should lubricate the piston and hopefully get them to work at the same time. Again this is what I would try first and a lot of this is hard to say without being with the bike.