I've heard that sometimes the support material is made to be water soluble, or at least weaker, in order to make it easier to remove. Therefore it could fall apart with age.

Are you sure that the model was not too large, so it added support material because it couldn't do it all in one go? (Sometimes even though the size limit is x by y by z that doesn't mean it can do something which is x by y by z all in one go.)