About FPS, it is interesting that in the game it can drop in any place where the game considers that the map has changed. And not only where you clear the location of monsters "in the wild" and in the "abyss." But also inside the house. For example, when moving from the kitchen to the room, from the room to the bathroom/hallway/toilet.
According to personal experience, FPS decreases to 1/2 or even 1/3. But if you make any other window active except the game, and then make the game active again (it may be enough to simply minimize and maximize the game itself), FPS increases in an unknown way and the game does not "slow down" until the next "change of the game map".
At the same time, the setting "stable 60 FPS" only raises the FPS to 60 from 30, but does not affect the drop or recovery of FPS in any way.