With the Map 3D Autocad, I have been experiencing the disappearance of blocks already in a drawing.
We use a block that consists of a delta (triangle in shape) with many attributes.
When starting a new drawing and inserting a new block, the block can be mainuplated without a problem.
Going into an existing drawing and having to either relocate the block to a different location etc., the delta disappears, leaving the information (attributes visible). The only way to have the delta appear is to do a regen.
With all the previous versions of AutoCAD, this did not occur.