Crap. What is happening here? Clearly a leak and mold…but why?

Hey there. We just noticed this in our air conditioning closet in the garage. It has a vent so it cools the closet as well. The unit has been in place for two years and this seemed like it popped up rather quickly. (Central Florida) I have a call to a professional in and I’m waiting on hearing from them.

That area has both deduct Work for the return, and pushing the air out toward the rest of the house.

Any advance help would be appreciated! It is a two year old Diaken.