Currently our clan boss on UNM only has 

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what is seen here left to finish off.  I bought a key and proceeded to run another 11m damage just to finish the boss off and yet he is still standing.  Another bought key in progress.  

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Lets see how far this one gets - 

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So after having to buy 2 additional keys the CLan Boss finally drops.  My 11.8 million key was more then enough to finish off the boss but the game glitched and no damage was reported.  Normally my teams run perfect on magic affinity and never drop out early but there is that 1 in 10 or 1 in 20 that does.  This is the 1st time I have seen damage not properly reported and the boss remain standing when it should have been dead.  This was observed between 12:50 am CST and 1:14 am CST.  Hope this helps to narrow the issue down enough to provide a fix.  Guild name is Neverwinter Dragons