Head gasket time.
Man you got the James Bond Series tractor there. Don't start pressing those buttons you don't know what they do. Might light off an anti-tank missle LOL.
You should cut that grass in different directions too. You can see you cut it the same direction every time.
Hard to tell on the video, but I am cutting on a slope so big that I tried to sit on the fender to keep from sliding off the seat. When I did that the seat safety started to shut the engine off, so I sat on the seat and the mower backfired. She is an oil burner, so before the cut I added oil and the oil level was extra high. I don't understand the inside of an engine and how oil can leak into the cylinder, but I hope that's all that happened. The mower has worked perfect since then.
That little slope and the wide turning radius gives me a hard time cutting it any other direction, but you are right, that lawn has been getting cut in the same direction since 09/20.