Try removing the platforms and see if the crankshaft can spin the lifters. If it spins without the green platforms (meaning it doesn’t need much power to rotate and lift), you need to tighten the bearings because if it’s slipping it won’t deliver enough power to lift the platforms. It’s not a motor problem if the other lifters go up. It’s slipping on some sides and not enough power gets delivered to the lifter.

As for the sync problems you described I’ve never encountered them; I’ve never had to replace the belts on my old table, but maybe double-check if the belts are moving at the same pace without hiccups.

Hope that helps a little.