21:09:16.238: Output 'adv_file_output': Number of lagged frames due to rendering lag/stalls: 817 (36.4%)
Rendering lag caused by GPU overload.
https://obsproject.com/wiki/GPU-overload-issues
Set the canvas resolution even lower is the only suggestion I have. This machine is not really powerful enough to work effectively with OBS and run Roblox at the same time. Make sure quality settings in Roblox are also low, and limit the framerate in game if it allows you to do that.