Have you checked the dishwasher waste hose is not siphoning back water from the main drain connection? The waste hose on a dishwasher needs to run to the height of the dishwasher then down to the point it is connected to the main drain. It would have come with a horse shoe shaped bit of plastic, this needs to be screwed high up and the dishwasher waste hose runs up and over this to prevent the siphoning problem I suspect you have.
Rupert, June 2020
