Can someone explain to me when PoI supposed to be visible on minimap?

There's no rhyme or reason to it. Sometimes I hit the boss right away and the whole map lights up with PoI markers. And other time I clear the whole freaking map, including boss, and I still have to look for the remaining ritual or something blindly. What is going on there?..

you need to kill the boss AND activate all checkpoints to reveal the markers. it's not a perfect system since a lot of start-boss checkpoint maps are simple anyway and you found it all on the way and 4 checkpoint maps are the ones where you need the help, but it's something