Bossfight bugged/not finishable - Viper Napuatzi

Hy,

during the endgame fight against viper Napuatzi and after the first time her guardians stepped closer, it occured that she jumped somehow behind her guardian's line. After that happened she got stuck and wasn't damageable anymore. Even after logging in and out she was still frozen. The bossfight wasn't able to be finished.