I have the same issue, reloaded save and my npc was gone. Pressing the U key just says MIA survivor.

MIne all disappeared today. Not MIA just outright gone from my roster. Like they never existed.

Whenever I press remove MIA survivor it says error

Same for me. WTH!! 3 years and no awnsed ;-;

yes this happens to me as well... trying to find a fix

I only have this happen when I reload saves or run a save on a new system. This is what I figured out....

The mod makes save folders that correspond to the save folders the game makes, but those don't transfer automatically to a new system, just the base mod. Renaming the save doesn't rename the folder in SS with the info to that save, so the mod sees it as a different save.

If you played more after the backup and died, or they died, they might just be gone. This mod saves it's own save folder in the SS mod folder that keeps track of the SS stuff. So, when you back up a save, you need to backup the same folder in the SS mod as well.