Only washing top rack

I would check for a water flow blockage in the pipes.

it would be improbable that you put too tall an item on the top rack every time you wash, but it is also impossible to check without a see thru tub. Just make sure there are no tall items and maybe lower the top rack.
Some dishwashers have the top arm on the bottom of the rack and use a connection in the back when the rack is pushed in. If yours does make sure it isn't deformed and not making properly.

Make sure the center loading is not obstructing the water jet to the top shelf. Top shelf is only for glasses and saucers , use Jet-Dry .Pre rinse and clean bottom pan strainer from dirt debris.

Position the spray arms in a certain position. Activate the dishwasher for a few seconds and then examine the position of the spray arms. If the upper spray arm has not moved, then either there is no water coming to the spray arm or the spray arm is clogged.

In my experience, you probably have a clog in the spray arm/arms for the top rack. Take the arm(s) out and see if the holes in them are clogged. Rice, plastic wrappers, and glass from dishes that broke in there are the most common culprits I've seen.

Make certain you do not use dish soap when rinsing the dishes. Make sure you only use DISHWASHER soap when running the DW.
In fact,there is no need to rinse dishes. Remove visible scraps and put them in the DW. If it is a quality DW it will clean your dishes. Do not crowd the dishes in the DW. Most JennAir DW's are quality. Make sure the top rack can get washing action from the bottom spray arm. No pots or other water stopping utensils on the bottom rack.

HI,

The top rack is not cleaning because of low water pressure from the wash motor to the upper spray arm.
Assuming the top spray arms are clear of debris, remove the lower spray arm to access the wash motor. Remove the 4 torx screws and the filter (accumulator assembly). Remove the torx screw and the inlet protector that covers the chopper assembly. Make sure the chopper is not broken (broken chopper will fill with debris and block water flow). While holding the chopper blade, reach inside the "D" shaped opening on top of the motor and spin the wheel/motor by hand in each direction to make sure either the chopper gear or the motor gear that drives the chopper is not broken. Replace the chopper if necessary . If the motor gear is broken, replace the sump and motor assembly . Remove any debris from the sump area in the process.
You don't have to shut the power off to the dishwasher because the door will be open, but if you feel more comfortable, do so.

thanks,

Yes there is the Water Div valve, it diverts the water between the wash arms.

Check to make sure the upper wash arm is not plugged with debris. All Plates on the bottom rack and bowls on the top. Position the arm at 12 o'clock and check at the end of the cycle to see if it has moved positions.

It is important to know that the upscale LG diswashers alternate between washing the top and bottom rack. So it is normal for some arm to not be turning at certain times.
Also, if this dishwasher is set to half load, bottom only, the top arm will never turn.