Sortie Rewards Bugged?

[RedShiftZero]

Three days in a row, I have duo'd the sorties with my friend. I have 6 rewards left unchecked, she has 5.
Three days in a row, we have both received fusion cores as a reward.

We are both missing the Latron Wraith barrel and blueprint, and some lenses.
There's been nobody else in the squad. I.e. nobody rolling rewards we already have.

Why do we keep getting cores?

[RedShiftZero]

Just had this happen again, duo with a different friend who is missing a Nezha piece, and a Latron piece.
In a squad with three people, got my last Latron piece yesterday. I now have everything except four lenses.
Just now, nobody else in the squad, both of us got cores.

Could this perhaps be caused by being in two-person squads for sorties?