Got the same issue on the Exiled Lands so this is a general problem and not just related to a particular map.
The thing is, if you have a save file from before this problem and you are resuming your game, the base is shown just fine (my base in the Exiled Lands consists of an estimated 100k+ pieces). However, quit the game and reload beyond a particular threshold, and your base is gone.
This doesn’t have anything to do with what the machine could handle (in fact, if physical memory is running out, the game simply unloads pieces of the map that are far away or simply starts swapping parts of the game’s code and/or data to the hd) but some limitation with the routines that handle saving the game’s data. When exceeding a certain size of a base, something seems to get corrupted while saving, and an attempt to restore from save is met with a failure, thus causing the base structure to vanish into thin air.
Anything that has been attached to the base (chests, torches, even workshops, stables, thralls, etc.) are afloat where you have initially placed them, and once you come into proximity and an integrity check is performed, they just vanish into thin air.
However, if you have multiple independent bases strewn across the map that consist of 100k+ pieces in total, they still remain if each of them is significantly smaller in size.
However, for this they need to be completely independent from one another - branching out from a particular base and then building at a new location won’t help even though you may break the linking pieces as they still seem to be associated with one another.
For example, if you have two hills that are close to each other and want to construct bases on both, they are going to remain intact when you first construct a base on hill A, then move to hill B and start a fresh build there without scrapping base A. Even though this sum may exceed the limit of pieces that causes your huge base to vanish, they are still going to persist since each of them is significantly smaller.
However, start a base on hill A, then build a bridge to hill B and continue constructing there, you are asking for trouble once you are exceeding aforementioned threshold.
So when making an educated guess now (the symptoms are quite indicative here), this happens because in the former case both bases have individual roots (and therefore most likely independent metadata structures referencing them) whereas in the latter everything is associated with the same root structure.
I have already issued a report on this as well, and it has been received. However, debugging this kind of issue can be quite tricky as you have to figure our where in the game this problem is introduced. This doesn’t have to be the part that is causing the problem to eventually surface.