Horrible smell 24 Atlas

We’ve recently noticed this putrid smell coming from the vents in our 24 Atlas. I would say it’s a mix between mold and fish. It only comes on for a few minutes when the car is started and goes away after running the air for a while. We’ve replaced the filters and checked what we could, but the smell will not go away. Has anyone ran into this issue, if so how did you fix it? Please help!