I'm not entirely sure how to describe this issue. It's not 100% consistent, but for the most part it works like this:
The wandering "prop" NPCs that walk all over the First City seem to disappear and reappear randomly. At times it's like there is an invisible line a certain distance away, and when they walk beyond that line, they disappear. If I run towards where they are, they will come back into view, but not always. If I stand still, they tend to disappear when they are a certain distance away, say 50 feet perhaps.
Its like there is some weird framerate limiter at work that draws and undraws the NPCs randomly to preserve FPS. Unfortunately I didn't turn any such thing on, it only happens in the First City, and don't know that it's even necessary for me.
It ends up making the city feel like a ghost town.
I do not see this issue on Holodeck, or on any other Tribble area, not ESD nor DS9 nor Defera nor Klingon Academy, only First City, Qo'nos, and it started with the Nov 17 patch.