OK, if you notice black marks even after cold wash cycle and cleaning the drain pump filter then try this:
Use 2 cups of vinegar (1 in drawer and 1 in drum).
Select an empty wash cycle on its hottest setting.
Let it complete and then wait for around 1 hour before opening the door.
Clean the drain pump filter located at the bottom front of appliance and clean the drum and door seal.
If you have ground coffee (you may pour it in a bowl/cup) and leave it for few hours inside the drum.
Then next day after all this is done select another empty wash cycle on its hottest setting with washing machine descaler or detergent.
Let this complete then, leave it unplugged few hours this time with door open.
The problem should be resolved now and there should not be any smell or black marks.
Let me know how it goes.
If you have any further questions, please do not hesitate to ask!
If you are satisfied with my assistance, your 5 STAR Rating (from top of this page) at this time is appreciated. Thank You!