The CO2 not re-setting is one of the primary symptoms of shelling-out to the desktop, along with a "steam" trail that might follow your boat, or a stuck external sea noise. There are all sorts of little anomalies that point to shelling-out, whether animation timings, audio, transparency, stuck weather, etc. Anything in the game can and will go wrong when shelling-out. You can somewhat minimize the issue by pausing the game and then using the Windows key, but you will still eventually encounter issues. The more RAM and the stronger the CPU of the computer, the better it deals with the issue, but you will still eventually run into issues. The game was written to the WinXP paradigm, and knows nothing about sharing resources or that Windows might move it around in memory.
I would recommend changing the hot key for OBS recording so that you do not have to shell-out for that task. I would also suggest investigating whether or not OBS is overloading your CPU and causing the CTDs you are experiencing, even when not recording and it is just sitting in the background. There is all kinds of info online about that. Also, always run SH4 and OBS as Administrator. You might also see if maybe the Windows GameBar, or the capture utility for your video card can do a more efficient job of capturing for you.
