Kitchen disposer with standing water

Trying to solve a kitchen conundrum. Our 6 year old disposer has about 4-6" of standing water at all times. If i turn on the sink faucet, the water rises and only subsides if i turn on the disposer (though it only drops as low as the 4-6" level).

I thought it might be because of the p-trap that looked like it had one two many sharp turns, but I replaced the trap and outlet with PVC and it didn't help the issue.

I thought it might be because of gunk or an obstruction in the pipes, but a gallon of Drano and 3 gallons of boiling water didn't help the issue.

My latest hypotheses is that it could be either:

1) Something clogged in the disposer (e.g. food particles in the basket of the disposer where I cannot easily access).

2) Something clogged in the air vent above the drain.

Any thoughts on how to troubleshoot before I replace the disposer and demolish the walls and replace the entire waste line?? :)

Thanks for any help!

The only time I have seen this is when the drain line from the disposer is BELOW the drain level through the wall, or if you have a double sink, the disposer drain is below the level of that sink drain.  So, water from the double sink will flow into the disposer, or water from the drain will also.  In other words, you are trying to push water uphill.  Which the disposer can do when it is turned on, but not when off.