The corrupted mementos you get from killing mobs convert to displaced corrupted mementos when you leave the vision and return to dornagal via the gate in the rewards chamber. It should even show a line of text in chat that says you receive an amount of displaced mementos exactly equivilant to how many normal mementos you picked up in the run once you zone back to dornagal.
It’s confusing, not sure why they didn’t just have mobs drop displaced mementos directly.