I think I discovered the cause: there appears to be a complex script system involving the doors that enables and disables the NPCs in each subsection of the Strip. I think the lack of activating these due to using fast travel markers inside the Strip added by mods is what is causing this problem.
Anyone have any ideas on how to fix this?
EDIT: I found a fix. I set up another "bug fix potion" of sorts similar to my Veronica fixer, and *POOF*, the missing NPCs reappeared.
Doing some more investigating...
In the mean time, don't use fast travel markers to the Strip proper. Maybe some time a modder can strip out the system obviously meant for optimization and just fill it with a lot of NPCs, since, as Sawyer put it, "memory isn't a concern for PC players."
