This issue occurs when a hero unlock is acquired in a summon for a hero that has already been unlocked.
The following hero unlocks will award the wrong number of tokens in such case (this is based off the fact that 1 star heroes should award 10 tokens, 2 stars 15 and 3 stars 25):
- Bramble (awards 35 tokens instead of 25)
- Yokozuna (awards 25 tokens instead of 15)
- Overlord Executum (awards 10 tokens instead of 15)
- Ignus the Mad (awards 15 tokens instead of 25)
Note that there could be more, but these are the ones that I noticed. Except for Ignus the Mad, the unlocks were all obtained through heroic summons (I have much less data with full unlocks in honor summons).