Edit: welp, I was so excited about writing a bug report that I didn’t take the time to see if this would happen after closing and reopening the game… It doesn’t. Looks like this is either a one-off problem or an intermittent ‘certain spots on a map causing framerate drop’ thing and unfortunately I can currently only say it’s the former 
Playing monoliths I am getting a massive framerate drop on the Fallen Harbour map and it seems to be tied to a specific point on the map. The closer I am to this point, the lower my framerate from my usual solid 60 down to 2 or 3. Generally my framerate has been really consistent since the latest patch which made this framerate drop much more noticeable. I am playing on ultra graphics settings.
Log file:
Player.log (231.5 KB)
System information:
DxDiag.txt (95.9 KB)
Screenshots to show location and framerate drop linked to proximity to a certain location:
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Hope this is the right place for this - I found another thread about slowdown on this map but it had been closed due to having had no replies. This isn’t stopping me from being able to play but hopefully it might help you track down the cause of this framerate drop 