Yes all of the assets from the various packs are still in the Content Browser. And I’ve tried restoring previous versions of the level files, but there aren’t any options to choose from.
So you’re thinking that it was just a coincidence that somehow the level file reverted back to a much earlier version, where over half the things I built weren’t there, at the same exact moment when I added this new light pack? I suppose it’s possible, but over the past couple of weeks, I’ve opened, closed, updated, and saved this file (and two backup files) dozens and dozens of times with no problems at all.