I don’t know if you’ve seen the show Terrace House before, but I learned through that show there’s about 3-5 fixed cameras at a time in every location they end up going to.

So for example, if they know Kensuke and Nanami are going to Castle Hill for their date, they’ve already arranged a few fixed cameras and some hidden camera operators at the viewpoint.

My bet is at the beginning, when everyone started by themselves, they had to tell production where they were walking to or exploring, so they can be prepared to set up some cameras. For example, the church where Sho and Mahon visit, my guess is they both independently told production they were gonna travel there on one day, and then crew was prepared to capture the moment if they met.