When i load the game i get low fps in some rooms, Machine room, Storage room, even a small room with lockers. But sometimes when i restart the game, the fps stays at 60 and i have no issues. I was wondering what might be the source of that problem.
If the game is from steam do a file integrity check, there might be corrupted files causing errors and thus lags.
Apart from that, I had this issue too back when I was playing Penumbra. You just need to leave it for 1 minute or so when entering laggy rooms and the fps will rise. It's like it needs some time to settle in some occasions.