Soap Bubbles in Dalton when Washer is emptying

I recently installed new Dalton ADA Height toilets in a rental unit. The one on the 1st floor is next to the laundry room. The tenant claims soap bubbles appear in the bowl after running the washer.

There's no water on the floor and seems to be fully sealed. Flushing does not appear to be a problem and the bubbles weren't noticeable on the old 5 GPF toilet.

Does this indicate a blockage or poor venting?

I would say that it is poor piping or someone is using too much soap or both, newer wash machines are prone to use less soap then the older ones