A few weeks ago there was a bug where coins did not appear in chests. Well tonight it happened to me again, just once so far but if it happened once it likely means the bug is back.
What kind of chest were you opening? A ranked chest, or something from the store or season page? This sort of thing might be best addressed via a support ticket – could you message us there with some more details? We’ll do our best to track it down. Closing this post so we don’t talk too much about your personal account here and can dig into the details through our support channel.