Misfire
The most common problems are either a clogged drain that allows water to back up, or a kink in the hose that allows the water to back up into the air gap.
Run your disposer (with running water) for a few seconds before running the DW. When the DW is running, check the hoses for kinks, even minor ones. Some hoses will collapse when heated by the hot water from the DW, but not so apparent when they’re cold. Any constriction at all will cause water to back up through the air gap.
If a hose is the problem, replace it with a thicker hose that won’t kink when heated.
