I noticed that if I am close to tethers and refilling my oxygen, fps would drop significantly. I also noticed that the more tethers I have the worse it gets. For example, I placed tethers very far from my spawn point and the game got very laggy (only if I am connected to tethers).
I am playing the game through Steam.
Specs:
16GB RAM
GTX 970 (Newest driver)
I7 4790K
OS: Windows 10