@Wayne-TP 

It seems the mapping wasn't completed. Can you send the vacuum to clean that area? No, I cant. I've tried zone cleaning the grey area and the vacuum wont go there. I've also tried putting the vacuum in that area by carrying it to it and it does nothing.

Try to send the vacuum to clean the Big Living Room, observe whether the map gets updated after the cleaning is completed. *Note: make sure the map isn't locked. The map doesnt update itself

If room cleaning doesn't work, you may need to do a whole-home cleaning to update the map, or simply do a re-map. I've done a remap (mata mata map 2) and in this case room 2 i.e the dining room in the old map (mata mata map 1)  is being greyed out and the vacuum won't vacuum there either.

  @Wayne-TP 

Yes, the map in unlocked.

Is the unrecognized area greyed out immediately right after the mapping completes? Yes, after mapping completes

Grey out after saving the map? Do you mean when it prompts to lock the map? If so no. It happens when it firsts maps out the room.