Washer leaves a large deposit of black material on sheets after washing

Clean clean clean at least once a month with recommended cleaner for your particular washer, make sure to run cleaning cycle in empty washer at first, then maybe a hot cycle with old rags/ towels you don't care much about. Also, some liquid softeners can leave marks. Try cleaning first, then with towls/rags. Don't forget that if you have a front loading machine black mold can form inside barrel, or the grey rubber that seals the door and machine tightly shut.

A buildup of detergent residue can occur in the wash tub over time and can lead to a mildew or musty smell. The TUB CLEAN cycle is specially designed to remove this buildup. Press and hold the EXTRA RINSE button for 3 seconds to activate this cycle. The display will show a message to add liquid bleach to the dispenser. After the cycle has ended, open the door and allow the drum interior to dry completely. NOTE: Do NOT use this cycle with clothes, and do NOT add detergent or fabric softener.

I think you model has a tub clean mode. i would try to do that. basically no clothes, no detergent, just fill the bleach dispenser and run the tub clean mode. press power and then hold in the tub clean button on the right for 3 secs. then press start.