I deleted my standard deck, even remade it and I am still getting this error. The only change I made was adding in the golden dragon from the tavern brawl this week.
Unfortunately, this is a double award visual glitch. You only get one of each Golden card.
The bug is that the Card Collection shows two awards of Golden Bronze Herald or Golden Recurring Villain.
The workaround is to restart Hearthstone.
This has been reported and in future when you do find a game bug:
- I have had the same issue and tried all work arounds above (remaking, editing, resaving, copying, checking for dupes, running repair). No result.
- Downloaded Hearthstone on my iPhone, opened deck, saw that althrough it appeared correct on my PC, on the phone the duplicate / ungrouped cards showed as well as the deck being short of 30. Removed the faulty cards, added them again, saved deck with 30 cards.
- Opened on pc. Worked perfectly.