So i run Ice golem level 19, i finished it in 44 minutes. All good. 

I run ice golem level 20. i finish it in 46 minutes no reward. Also my playtime reward didn't updated. You get no reward screen, just spinning arrow. I run ice golem 10 times so its like wasted 10 hours, and not a single time i got reward or game registered play time. So yes its a bug.