I added the pack the same way as I did all the others. I clicked on “Add to project” and selected the project I’ve been working on.
I guess it’s possible that I overwrote content, but I’m pretty sure they didn’t have the same names. As I said, whole sections of the map were gone. Walls, floors, consoles and chairs. And none of those object names were in the new light pack that I added.
Another strange thing that happened, just after I added the new light pack to my project: I opened up the project and opened the specific level I’ve been working on. Normally when I open a level, everything appears all at once (without any delay). But this time, objects (walls, ceilings, etc,) started appearing one at a time (as if slowly loading each object) but then it never finished opening the entire latest version of my level. It appears that the level that opened, was one of the first “saves”, from the first or second day I was working on it. It was like it opened an early version of the level.
I’ve been trying a few things to get the project back to the way it was before adding the light pack. I deleted the project, then went to my computers recycle bin and restored the project. This restored much more of the level, but still not the latest version of how I saved it yesterday. I should also mention that I moved all my projects/levels to my D drive, several days ago (everything worked fine), because my C drive is an SSD and I didn’t want to keep reading and writing to that drive (SSD have limited read/writes), so I moved it to my HDD D drive. Just thought I’d mention those things just in case they might be relevant to the problem.