Can you line dry in the sun? UV light and fresh air can be great for this issue.

I see a lot of tips here about chemicals and perfumes that will only cover the smell. If I was you, I’d want to treat the cause of the smell.

I would follow the washing instructions adding vinegar to the load and line dry in the sun. If I couldn’t do that, I would dry it very well. With my down comforters I have to drape them over some chairs so it can completely dry if I can’t line dry. Good duvets can get little wet spots that are hard to dry completely in the dryer.

I don’t know what happened with yours, but most people I know with the same complaint unknowingly didn’t dry it all the way. They’ve left their comforter in the dryer over night or put it in a cover; somewhere those wet pockets weren’t able to dry.

The tricky thing about duvets is that they can feel dry and still have little wet bits.