Hello,
I just tested this, and, yes, if you close the myoboku trial game interface with the escape key while playing the game, you will lose that attempt. Unfortunately, this is not really a bug. You will need to be more careful in the future and make sure you do not close the game interface while playing, as this will result in lost rewards. Sorry about this. :(

If you are saying that you lost multiple game attempts, not just multiple hammer swings, that would be abnormal, yes. You will need to submit a CS ticket to see if anything can be done about this. Here is the link.

https://support-center.oasgames.com/