I run a "clean washer" cycle when the reminder light comes on.

I use Affresh for the first cycle.
Suds come out the top hole in the back of the washer.
The cycle completes normally. There is no error code.
If I don't use Affresh on the first cycle, I still get suds.

I run two more "clean washer cycles with no cleaner.
The suds are much reduced by the third cycle.

I never have excess suds during normal washing.

I suspect that something in the tub is accumulating detergent during normal washing.

What could it be?