It’s a bug, see my reply in the next post
I had been saving up my Fit Stones so I could evolve a hero to 7 stars but it seems I don’t have the necessary advanced powerup for that. Instead, I evolved a different hero to 6 stars so I had 160 Fit Stones remaining. I noticed that you could add an active skill when evolving to 6 stars (though that was me just noticing it- something to add- a notification asking a player to select which additional active skill they want upon upgrading as I went for over a week without adding these skills to prior evolved heros). I knew that passive skills could be replaced and was looking at the different skills they could be replaced with. Doing that, somehow I actually made the replacements!? However, the I don’t see one of the replacement skills I know I was looking at (HP III). I didn’t even know I was doing it until I got a notification that I didn’t have enough currency and I freaked out as now my 160 Fit Stones had been reduced to 10! I don’t even have the skills I would have selected if I knew I was going to be spending the Fit Stones!
There are notifications in the arena for each time crystals are spent, perhaps the same could be done for Fit Stones? Or make it a settings option to have notifications turned on and off before spending the different currencies? I’ve been playing the game quite a bit and have upgraded and replaced skills before so it surprised me to see what how easily this happened unintentionally.