When you equip Hammer of Wrath, it incorrectly adds an additional +1d20 damage die. The correct functionality is to convert the d10 die to a d20 by spending 1 Stress prior to attacking.
The bug appears similar to the Brawler’s “I Am the Weapon” where it shows 3d10+1d20+7 (separate damage dice).
Thanks for the report. I have a ticket open about this currently so I’ll get your report added to that!
Edit: Actually I checked on the ticket and this part of the problem will be fixed in the next patch. I believe we’re still working on getting that 1d10 to update to a 1d20 when you spend Stress though.