I think i know this spot, and it has been reported with screenshots, and maybe even videos before. i can’t find it tho.
here is another posts about it i could find: Bugs discovered from playing until now
But i am pretty sure there was a post with a collection of screenshots, this happens in multiple spots. One i encountered it the most is when u climb down the ladder in the small tower left of the bridge from mariners keep to sacrament. there is a ladder u can take to reach the shore and water below (the spot in the screenshot above i believe). it happened multiple times to me there.
i found a video i captured myself tho 
sadly i have no footage of the other spots. one was i think at the bottom of the “2 way” elevator. when sending the elevator next to the bridge up and then take it to get down u can walk across a small section of wooden floor. between evelator exit and that floor is another insta kill spot.
EDIT: my footage is from an earlier built, captured june 23rd. It happens not every time, seems to be random/sporadic and has nothing to do with running out of stamina or something like that.
Hope that helps