i was on the convalescence budding mission for the exotic microcosm , me and my 2 clan friends ran the mission and he got the reward at end of mission but i didnt , i looked at quest tracker and still says i have to complete the 3 instances which we already did and he got weapon am not getting the credit for doing theses and its not a quick quest chain either .
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The comment by viiTactiiCZz is correct, you may need to redo the mission.