It's happening to me aswell. On S5 Rock Lee. Manda just keeps biting, everyone is just standing there doing nothing. No other attacks from either Manda or my ninjas. Just the darn biting.

I get Orochimaru down with everyone having full hp + shield from Iruka. The first bite from Manda does't kill anyone, but then he just repeats it, killing everyone one by one while they just stand there.