Good chance a capacitor or two are failing. Might just need a cap kit. Before doing that, try rotating your vertical size pot all the way clockwise, then counter-clockwise several times to kind of "clean" the carbon contact area of the pot. Sometimes the contact area gets iffy from staying in one spot too long, and the resistance will jump up and down a bit. Try the same with your vertical position pot, but appears it's expanding and contracting in the vid (on my cell screen anyway). If there's a cracked solder joint on one of those pots, it could cause a similar issue.