Odd, the chest at the end of the mission dropped mine, and another at the end of the Legend clear, so not sure why yours didn't. Maybe you will need to complete the mission on Legend mode for it to correct itself, but not sure honestly.
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Ran the mission on legend and got a non-redborder one but the initial quest popped back into my inventory and allowed me to talk to eris again which gave it to me so i guess legend fixed the issue.