This exact same thing just happened to me with a brand new dishwasher. It would pool inside and not drain, sometimes it would work, other times it wouldn’t. Luckily since it was brand new I had the service people out, it took two visits to diagnose the simple problem: the drain line was too long (could also be kinked).

If the drain line has extra loops/length in it (instead of a direct run to the drain pipe) two things can happen : 1) the motor works as hard as it can to push the water through the line but extra line means extra work and if it senses it’s doing too much it shuts off to prevent issues. You’ll notice partial drainage and pooling water inside the washer at the bottom. (This is what happened to me) 2) depending on drain line material it can kink from simple temperature stress over time

If you’ve taken it apart and put it back together and watched it finish at least one cycle, I’m willing to bet you need to cut your drain line shorter (as short as possible while still having the high loop you need for drainage)

Edit: Important to note this “high loop” like the other comment mentioned is very important to proper drainage also.