Later in the game you need to get two samples of Lot 192 to break the last of Fontaine's mind control over you. The problem is that if you have the unlimited items trainer option activated at this point, the game registers you as carrying 100 Lot 192s. This means you cannot pick up the second one later, and the game won't progress.
Advice: deactivate all trainer options that affect your inventory while you complete the Lot 192 quests.
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