This I believe is an inherent characteristic of this pour, I see this a lot , areas where they get to the end of a mix during the install, smaller and less aggregate pieces with more of the base material showing thru. This cannot be corrected short of demo and re pour. Unfortunately terrazzo restoration will expose every sin of the installers, this is common and I always tell customers going in, in fact I can usually find a area like this before I start especially on outside walls. Just like all natural stone has inherent characteristics ,so does almost all terrazzo