This isn't a bug per se, sometimes there are connection problems which can result in the game taking a lot longer to play than with a better connection. Or if the opponent disconnects it can appear to freeze until it looks like they've dropped out of the arena.
Unfortunately things like your internet connection or that of your opponent are out of our control so there's little we can do about it. If you have further problems save the battle ID and send it to one of the mods just in case there's any fishy business going on. lupos at ateil dot com , logress at alteil dot com are the best to email first.
As for Kurina and your monk, Kurina needs to go first in order for the Monk to get the +10 Attack. Since your monk went first he attacked normally.