" * Defeating Toe Knee too quickly will no longer prevent the encounter from continuing."
Whatever you did (if you really did anything) it’s of NO help. Several times today as a mage I tried to kill both bosses completely naked. Gradually lowering the hp of Toe Knee first and then Mrrgria. When they both started attacking me, I killed her first - she got stunned with 1% and then tried to kill Toe Knee. But he got stuck with 1% hp and was very much alive and kept chasing me around that theatrical stage.
FIX that BUG!