Thanks for the reply. Everything is updated so that's not the issue. Whenever I play ComeCloser I always experience this low FPS problem (massive latency spikes, reprojections, low GPU utilization). If I switch to any other VR game (HL: Alyx, Contractors, H3VR, Boneworks) I can consistently achieve steady 90 fps.
Does it make any difference if the game has not been added to the Steam library and is launched directly from its directory instead?