Never encountered this bug before till now. I jumped from a ledge to another area and I fell through the gaming world. Its now happened a few times; I get out of it by fast travel to another location. Its annoying and it cost me going back to finish a side mission.
If you can provide some videos highlighting the locations you experienced this I can forward them onto the Far Cry 5 team. However please note there are no further updates planned for Far Cry 5.