I used the hear them a lot in the 2010's, and -- before that -- in the early 2000's. Then nothing after the last cycle dipped. Recently, I've heard them only 3-4 times, weakly, since the solar cycle picked up. The chanting is a game -- one guy tells the other when to start chanting, he records it, plays it back. I think it's their way of hearing how their radio gets out, something like that. A contest of sorts. Nothing religious about it. It's a sort of game. Listen closely, you can hear the pause, and then the playback.
I think most of them are in Kalimantan (Indonesian Borneo). If you hear them just talking, when you hear the word 'ganti' it means 'over'. It's Bahasa Indonesian, Indonesian Malay.
In 2012 or 2014 I heard them for several hours one morning (Pacific Time) when the conditions were really good. Some guy in Kalimantan was chatting with a young woman in the Philippines. When I was hearing them every morning, it was all between 6950-7040 kHz or so, they didn't seem to go too far up the 40 Meter Ham band.
There are also legit, Indonesian hams that hang out in the 40 Meter band between 7040-7100 or so, and they're on at the same time -- or at least were back in the 2010's. Haven't heard too many of those recently, but I'm sure they're still running ham nets at those times.
Mostly heard (back then and recently) between 6999-6030 or so.
But this solar cycle, not so much. Poorer conditions than the previous upturn 11 years ago.
Location: NW US, WA.