I haven't read all the posts in this thread, but I would have the main drain line from your house cleared.

If the main drain line is partially clogged, you could have water backing up in your drain piping every time the water spins.

(The washing machine drain is the canary in the coal mine when it comes to judging the extent to which your drain piping is working properly because no other appliance or fixture puts as much water into your drain piping as quickly as your washing machine.)


What very well could be happening is that when your washer spins, the water backs up in your drain piping, but not enough to come gushing out the washer's stand pipe drain. As that water gradually drains away, it could create a partial vaccuum behind it that could suck the water out of the washer's stand pipe P-trap, leaving that trap empty.

It's always a good thing to keep your drain piping clear, so if you can't remember the last time you had the main drain line from your house cleared, it's a good idea to have it done regardless, and it very well could correct the problem you're having with the washer's stand pipe p-trap.