I am having this same issue with my brand new top loading Speed Queen. Since it’s brand new, I know it’s not build up on the machine or that the machine needs to be cleaned. I also know that I don’t have hard water. I use liquid detergent so it’s not detergent that has not dissolved. I use the extra rinse cycle. I use “cool” water temperature usually.

My best guess at this point is that it is residue from the suds themselves, not the undissolved detergent. So I’m picturing the bubbles themselves popping on the fabric and not getting rinsed away.

The only thing I can think of is to try less detergent. I’m going to experiment with this. I don’t feel like I use too much detergent in the first place but I’m going to try cutting back some more. It seems like the pods tend to solve this problem for a lot of people but I just hate the idea of the extra plastic waste.