Try pouring some drain cleaner down the stand pipe. Be sure to follow the products directions for how to use. Check pipe compatibility. Drain stand pipes should not have a bunch of elbows back to back at the bottom. Eliminate as many of the turns the pipe takes as possible.
Some machines do a better drying job than others.
Remember that most machines use a blow dryer method with heat. Dish that have deep pockets or rims will often pool water, the dry cycle can not disperse this accumulation of water. The round design dispensers have a couple of tabs that stop the door when released, these tabs are molded into the body of the dispenser. Check if they have been broken off. If so replacing the dispenser should resolve your problem.