First of all, love the DLC, love the game, thanks for all you do! This is a consolidated bug list from reddit.
1. Traits are not awarded upon defeating a legendary lord under the effect of Eltharion's capture mechanic.
2. Gambling for Winds of Magic in campaign is not working properly: the amount of Winds awarded does not change.
3. Azhag's Vanguard trait should affect all orcs but does not affect Black Orcs. Other skills in his tree state "All Orcs..." and it affects Black Orcs but the Vanguard trait does not affect Black Orcs.
4. Going into Raidin' Camp stance with a Waaagh! army accompanying will raid one of your nearby regions instead of the one you're actually standing in. Specifically the one you started your turn in
5. Goblin Big Bosses lose their mounts when entering battles, even thou they are mounted (be it wolf or spider mount) before entering the battle. I have switched Goblin's mount back and fourth before and feel its causing the bug to appear on all armies, not just the attached goblin's army.
6. Norscan chieftains' skill trees are not displaying properly
7. Greenskin Coop Campaign mechanics are not working properly (only one player can have a Waagh at a time, and Confederation is broken).
8. AI Black Arks appear not to be attacking cities, despite their newly added capability.
9. Eltharion's hands don't grip his weapons
10. Sometimes selecting a skill when levelling does not play the sound properly. Noticed this a lot on spells specifically
11. In Grom's campaign (Mortal Empires at least), recruiting Da Eight Peak Loonies won't unlock the Hell Pepper 'Shrooms-ingredient, even though the ingredient's popup says to "Recruit ANY Night Goblin Fanatic unit"
12. The pop up screen for upgrades stays on the screen.
13. In a co-op campaign, if one player has an active Waagh!, the other player stops earning Waagh points
14. When my army intercepted beastmen I could only use my waaagh units (4 at the time) with main army nowhere to be seen
15. Players lose Blacktoofs head permanently if the character carrying it dies.