your cpu is simply too slow for x264, consider upgrade to skylake to get latest version of quicksync and nvidia 900 or 10 series for nvenc
for now you can update to latest obs 15.2 , lower fps in obs to 30, try crf 23, and enable vsync in game
but if these two lines are still there
17:00:42.430: Output 'simple_file_output': Number of skipped frames due to encoding lag: 6022 (98.3%)
17:00:42.430: Output 'simple_file_output': Number of lagged frames due to rendering lag/stalls: 1690 (27.6%)
its bad, first is about cpu loosing 98% of your recording and second about gpu being too slow also