Hard to say but the first thing you want to check is the discharge. Run the machine and slowly lift out the hose from the drain pipe when it is draining and see if the water is rushing out.

If not something may be clogged in the line or in the pump, or the pump may not be working right.

A little late on the response and not sure if you have continued deal with the problem and keep the washer.... I have found the same issue with my whirlpool washer. Mine is a top load with the fabric softener on the left hand side and the bleach behind it... We been dealing with this issue for a year and tried many different rinses... And yesterday I noticed that I could lift the cover off the fabric softener dispenser and found a massive amount of gunk that looks identical to what we see on our clothes.. It was bad, so I cleaned it and rinsed it many many times using a q-tip to get under it better... But caution you then need to run rinse cycles multiple times and then do your first wash cycle with dark clothes as the problem increases... Before it gets better.. Good luck..