@motorsep Just got dragged in from another thread. I don’t think that your issue is related to this.
Back around 4.6 or so I made an open scene with a cave, that had quite narrow and long entrance. It was static lighting only and I did not remember having any complications. It was a desktop project though. I remember only enabling cast shadows as two sided on terrain mesh and unchecking lower hemisphere is black in skylight. Otherwise, most settings were close to defaults.