What you were expecting to happen, and what actually happened?
AI uses a Spell that grants an Extra Turn, if they get an Extra Turn on a match then they receive TWO additional Turns.
What are the steps to make it happen again?
Fight a Boar Rider, Goblin or any other Troop that grants an Extra Turn
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!
Nope, but this is easily repeatable (at least on Console) and always happens without fail.