Hey folks,
Something that we ran into last night was items in our mythic runs were not able to be traded. After talking about it at work this morning, we started looking into it further. We found this from the Watcher Dev Legion Q&A:
In Legion, if you get an item from a dungeon or raid with personal loot that isn't an upgrade for you (lower or equal item level for that slot), you can trade it to another eligible player.
So if you run into this scenario, here's your answer. Happy gearing folks.