In the near future we're going to make a slight adjustment to Healing Tokens. After the update, when a hero is defeated all the Healing Tokens on them will be removed. This only effects a few scenarios, such as Skeletons and teams that use Uneasy Sleep. It's a very low-impact change designed to avoid some extreme cases in which cards build up huge numbers of Healing Tokens.
We expect to make this change in the next week or so - there will be an in-game notice when the change is live.