I clicked on the red replace button in atlas and the atlas emptied up

[laurentl]

Blowing up a few hours of work so how do I restore that ?
(and why did it blow it up in the first place ?)

[pahe]

Hopefully you work with an versioning system, then you could simply revert it. If not (and you SHOULD work with a versioning system ) you have to build the atlas new. If you're not replacing the .meta file, then all references to the atlas should be still there.

From my experience the atlas generation may be corrupt when it couldn't access the atlas or the atlas is in a PVRTC compression.

[laurentl]

The version was older than me redoing the atlas so fortunately it didn't take long.