The brickwork might have been pointed in a manner that has led to the wall inadvertently picking up damage. This could be the case if, for example, modern cement mortar – instead of traditional lime mortar – has been used for the pointing.
The more modern mortar could trap moisture and so prevent it escaping via the mortar joints. This, in turn, would force the moisture to emerge on the brick faces, where it could be frozen and then lead the brick surfaces to crumble.
Have you spotted signs of damp in your home recently? Perhaps it’s rising damp, which decaying timber flooring or crumbling plaster can indicate. Alternatively, it might be penetrating damp, which can happen if water shifts from a high part of your home to another part further down.