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 (the week starting the March 28) - there will be an in-game notice when the change is live.