But, sadly, this bug still occurred several times, and brought me to several resets (obviously ruining my enjoyment of the game). So I quitted from the game and started the chapter again, thinking it was only a single episode. I tried to click on "start from checkpoint", but the screen became black and nothing happened (but the menu could still be opened). I also tried to press some random button, but nothing happened (except Kage, which once activated showed my character crouched and still).
Obviously I was killed fairly quickly, and then something else happened: instead of starting from the checkpoint, I "respawned" (even if there was no character) EXACTLY where I died, with the sentinels continuing their patrol and the camera freezing to the point where my character (or my corpse.) should have been. Basically, after starting Chapter II (of Nightfall), I noticed that, even when being extremely close to a sentinel, the stealth kill didn't work (as well as shadow kill and other stuff): basically pressing the intended button was useless.
But, sadly, this particular problem occurred. Recently I finished Nightfall, and now I'm trying to get the various "all medals" achievements of the DLC. I've been playing the game for several weeks and I'm really enjoying it, definitely a hidden gem. Greetings, this is my first post in this subreddit.