I have the "Fail to load file" issue. I have just lost a week's work, as I was constantly saving, but had no idea that it would ever not load. 
I am building a scene and have no avatars, no animation, and no issues with versions (using 8.5.3330.1). I had no issues with building, everything moved smoothly. 4090 GPU Helps a lot.
The scene is large, about 15 GB saved. But will no longer open again.
So I assume I have lost everything. Hope this helps identify the problem.

Also wondering if an auto back up system could be added, like up to 5 or 10 versions?
Thanks, Scott

DAMN. When I first read you, I thought that the large file load issue can happen, I had that from time to time when the file was 5-6 GB. But DAMN 15 GIGAS ???? What were you building, a whole country ?
Lol joke aside, what was in your project exactly ? How many polygons did you have ?
Iclone has grown more powerful over the years and can handle quite a lot of polys, but if you had textures at 4K (or more) added to a high poly number, it can causes iclone to crash or just not load the file because it is, indeed, too large and has too much data. Even Blender would have a hard time loading such a big file...
Let's hope everything isn't lost. Did you save some props ? Maybe I can help optimize them so the file isn't that large anymore.