I had this ACAD (LLD 2008) drawing this morning that would open and display the objects normally until the LLD project manager pop-up appeared. Either with or without a project selected, one more click and all the entities disappeared and I was left staring at a black screen.
Zoom all you want, there is nothing there. All the layers were on and thawed. Listing "all" revealed hundreds of objects. In the text window, for each entity listed, after the "layer" and "space" was the word "invisible".
Spent some time searching the internet and found out that ACAD provides the ability to make objects invisible. Found a lisp to change my objects back to visible, but they changed back to invisible after every save. Eventually had to wblock out the entities into a new drawing.
Yet another new and interesting problem from them ACAD folks.
Am I the only one who didn't know about invisible ACAD objects?