First things first, make sure that you are actually meeting the initiative requirement of the challenge (consensus is generally that this means at least one ninja on your team must have initiative higher than what it is required). If you are not meeting that requirement, than it is well-known and has been repeatedly brought up in forums that the fights will be all but impossible, with similar things like what you are describing happening.

On the other hand, if you are meeting the requirement/already knew about this (in which case sorry for hashing out the details :P) and this is still happening, then we have an actual problem on our hands.