I tend to suspect that one or two or a limited number of ArchiCAD elements may prevent the 3DS file from saving.
Does the saving process present you with an error message?
You could try to track down the problematic elements by making one layer visible and saving just that as 3DS. If it saves all elements on that layer are fine.
Then make another layer visible and save again. And by making additional layers visible and saving again and again, you can find at least the layer of the element which causes the 3DS not to save.
Then you can continue narrowing it down and finding the problematic element(s).
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