Same, I got this problem as well! One of my friend has this problem too and we've shared our concerns via forum and email. So far no one has gotten back to us whether it's been solved or not. Hopefully this would be resolved soon as I would think it's pretty unfair if we're getting 30% of the rewards.
I've had this same happen to me now at least 2-3 times. Eveyrything was fine until the latest update. Before it I used to get roughly the same amount of traces and coins, but ever since the update, roughly 30% traced, and about the same with the coins.
I didn't take too much notice on the previous times, but it looks like the other loot might be unaffected, or at least doesn't show as big of a disparity as the other two do.
Note; I was the host this time, however, as you can see from the picture, from the group of 5, 3 were unaffected, and another person in the group had this same issue.
Also, our levels were roughly the same, I'm on 63, so in fact the highest, level-wise anyway. The other one affected, the bottom one, also level 62.
What I've noticed, is that the other players "kills" and thus traces don't seem to be "flying" to me anymore. You know, those lines.
So maybe that is partially the issue, the game doesn't count the other players in your "loot"?