This seems to be an issue again. Anyone got a solution?
Ragdolling with C through the roof isn't working for me.
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EDIT:
I found a temporary solution until this bug gets fixed:
You have to have Sandbox Mode unlocked.
Aquire the keycard in Sandbox Mode (delete the door, then pick it up), then save the game.
Convert the Sandbox Savegame into a Regular Savegame. (see: https://www.reddit.com/r/Voicesofthevoid/comments/1c52tns/can_i_port_one_of_my_s... )
Load the converted Sandbox Savegame, put the Keycard into the Mailbox, save, then load your regular savegame and the card will be in the Mailbox.