Drywall issue (see pics): what could it be?

[Kate H.]

One of the houses we're looking at has some strange drywall issues (mold?). Has anyone seen anything like this before? It's in two different locations in the house, both facing the outside wall although there are no apparent issues from the outside. Does anyone know if this could be a serious problem or perhaps an easy fix? We're unfortunately not able to see it in person so our realtor provided us with these images.

We're still very new at this and appreciate any imput!

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