Hey there, I fear there was an overlooked mechanic because we forgot to enable the tutorial popup. You can use Cervius to interact with the mindcontrolled Sanguine units which will allow you to dispel the mindcontrol on them. This should make your life much easier in that mission.
As a side note, you can also get other stage skips items by crafting them (you get the special crafting material for those from the arena minigame)