I killed the skeleton in the Dragon Battle and the skeleton feel to pieces on the ground. The screen did not allow me to claim the reward just went to Refresh mana ??? please see screen Capture. I now have 4 screen captures of this at different times.

Which means that I have to wait 3 hours and then it starts again with a full strength Skeleton. This also causes issue with the Daily quests if you need to kill 2 to get reward. as you have to wait  9 hours to get 3rd go when it should take 6 hours.. 

 

Were the points for killing the monster added to your total?  If you killed the monster with your last mana, you'd have to wait for it to recharge anyways, so as long as you're still getting the points you don't actually lose anything. 

Refresh your browser or close out and relaunch SF from the app.   That works for me when I get this issue.  If I don't do it, I get the same problem where if I log in later, the kill never registered and I only have whatever mana was left when the bug happened.

Hope this helps.