You have to understand how these dual motor units work. When power is applied both motor are turned on but one motor may turn faster due to the load on that motor. If that does, the bed (or slide out) will move down faster on one side than the other. The instructions for re-sync are to let each motor stall out at the end of travel limited by the seats, bottom limit or top raising limits. I would suggest if you have not done so already to attempt returning the bed to the raised position, maybe helping the stuck side with a little push (while someone else is holding the key switch). If the position is way off to begin with, this will probably not work. Each motor needs to be turning and not stuck for this to work. By pushing on the side that is behind in it's travel, you are reducing the load on the DC motor, allowing it to turn faster.
I am an Electrical Engineer and understand how these systems are supposed to work but I have not had the out-of-sync problem go too far out of line as to get a stuck system. I have noticed that my system normally TRIES to go out of sync. This is why you have to force the motors to go all of the way, up or down, until alignment occurs at the stops built into the system. I do not like to run the motors until they stall in fear of burning out a motor but I think they have a current limiting built in to minimize this issue,,,,at least that is how the slide out motors are protected.
Hope this helps.