@The_Schwarz1 I am unsure how that particular players issue was resolved with an update.
There has been three different issues reported that are related to the quest 'Into the Fog'.
- Quest "Into the Fog" disappeared from the quest log [Fixed with update 1.3.1]
- Unable to unlock prison door in Tuam in "Into the Fog" [Fixed with update 1.3.0]
- Cannot loot key in "Into the fog" after clearing out the cave before accepting the quest [Could not reproduce/Unable to fix]
The issue where players could not unlock the prison door occurred when players had the prison key in their inventory but could not unlock the prison door. Also for the issue where the key could not be looted after clearing out the cave, the development team were unable to reproduce this as I mentioned previously.
There is currently a known issue that is being investigated, where if the 'Light-Fingered' skill is equipped key items are not collected, it's possible this is what has happened here. The workaround is to load a previous save, reset the skill then try again, however I understand this is not an option for you.
I'm afraid the development team would be unable to edit your save file to help you finish this quest.