I had the same thing happen!! I used a 3oC and a fireteam medallion at the same time. I never did more than 4 strikes in a row and then switched to either public events or crucible. The only reason I switched activities is that I think I read somewhere about diminishing rewards for doing the same activity continuously. I received a total of 14 legendary engrams, 2 illuminated engrams and ZERO exotic engrams. I wonder if the 3oC and the fireteam medallion don’t play well together and it screws with something somehow