Imo starting the boss encounter should immediately update your checkpoint to the boss room, but at least it's nice to know about this.
Respawning when dying in the Pit is the worse experience of late I have had with D4. Literally losing an extra 30+ sec on TOP of the 30/60/90 penalty, because you have to haul ass across the entire place to get back to wherever you died due to checkpoint system being flaming garbage, feels insanely bad.
or you know blizzard could not be lazy, and code it so your checkpoint is updated everytime you take a portal and more than once every 30 seconds.