I have spent all my career in the catering and food industry with dishwashers of all shapes and sizes.The usual reason for this can be two fold.First make sure that the bottom spray arm spins freely. For various reasons they can stick and that means the spray only hits one place. If you spin it, it should spin at least 2 revolutions. Even if it does....Remove the bottom spray arm. The thing that makes it spin is the angled jets in either end. They will often block with debris, and the worst is lemon pips and cocktail sticks, even fluff. No one knows how fluff gets in there, but it does. At my last job at a VERY busy airport lounge putting literally hundreds of baskets through a day, the two filters had to be de-fluffed every day. The problem at home is that the fluff solidifies between uses. So look at those end two jets, poke with something and put water in from the jet end rinsing to the big hole in the centre. Put the plug in the sink so you can see what comes out. The turn the arm over and force a good jet of water into the big centre hole and it should show as a good jet at the ends. Then put the arm back and make sure it spins.Your machine has a strange item called a 4 port diverter valve. This part concerns me a bit as it appears that it may be supposed to move or at least has to be in the correct orientation. Some items like this have a rubber flap that really does divert the flow. Once gain, some type of debris can ruin its function. It looks easy enough to remove.504 - Diagram Number FOUR PORT DIVERTER AND PLUG ASSEMBLY WD19X26398
https://www.geapplianceparts.com/store/parts/assembly/PDT715SYN3FSAnother trick is to whip the door open mid wash if it doesn't have a safety lock and see what the arm is doing and if it is spraying well.I hope this is more use than our friend Umar Waheed! We are getting a lot of the AI Chat GPT4 Points Jockeys! Usually after 40 to 100 answers, they ask "How do I cash out my points" :>D..