So, after some further play with the changed trade post, it definitely seems like something is up? I think the problems mentioned in the post (which OP told me persist no matter the IG time and drop framerate to 15 FPS) are linked somewhat to the vfx pack and how it is registering whatever is causing something I've been experiencing.
But even without the pack, there seems to be some new sun-like light source in the center of the trade post above the portal. I'm not sure if it serves a specific purpose or not, but I'm pretty certain it wasn't there until recently. Without the vfx pack on, it can still be pretty jarring if you have your camera raised to max height and walk by the center of the trade post. I did my best to illustrate some of what I've been seeing recently with certain camera angles. (I exaggerated the camera angle for most of these. I don't play exactly top down, but it is easier to see the effects like that)
Curious to know if that is meant to be showing up for players or not. I imagine if it is taken away, OP's problems will probably go away too (without them having to take off the vfx pack)