I had 50,000 blood echoes and died. I had other matters to attend to so I decided that I would just sign out and come back later to retrieve them. I go back to the scene of the crime and there was no blood stain... nothing... I killed all enemies in the area, hoping one of them stole them... no luck. I did not die a second time so there is no way I lost them that way. Any idea how I can retrieve my lost blood echoes?
I stumbled across this reddit post and it turns out multiple players have also experienced this. Turns out there is a way to retrieve your blood echoes. Go to the Lecture Building and, for some unexplained reason, your blood echoes will be in the room adjacent to the bonfire. I really hope this helps someone out in the future. Happy hunting!
I did a little experiment where I intentionally died, exited the game and continued. I can confirm that regardless of where you died, you can always go back to the Lecture Building (1st Floor) and find your blood echoes waiting for you.
You might now want to kill any boss, or you won't find them — at least that's what happened for me. I died to a chalice boss, signed off, came back the next day, and one-shot the boss. Echoes were not in the room. I searched the Internet, found that post, and went to the Lecture Building first floor, but echoes were nowhere to be found.