Since this has been confusing a bunch of people into thinking there are weird bugs going on, I'll explain what's going on with this:

• Korzan has an SP enhancement that costs 10 SP, which gives him 100% all elemental mitigation for 1 turn at the start of battle.
• However, in the arena, people have been seeing it last for 2 or even 3 turns. This is actually normal behaviour, but nobody's ever really noticed it (or at least complained about it) with other "[Buff] for first X turns effects". In fact, it's even applying to stuff like Lotus Manuscript.
• So Korzan's getting up to 2 extra turns. What's up with that?
  • Firstly, all enemy units receive 1 turn on "first X turns" effects - or rather, their duration only starts counting down on the unit's first turn. This is because otherwise they would receive less turns than intended on offensive effects, such as Zekuu's LS.
    • This actually applies to most buffs/debuffs applied to enemy units during player turns, and in reverse, too. The datamine shows adjusted values for some effects so it doesn't confuse players that an ATK down infliction might have 0 turns duration and still work. Meaning first X turns effects are some of the only cases where you're actually going to get confused.
  • The second extra turn is Omni Paradigm Level 3. This grants 1 turn to certain buffs, and happens to include elemental mitigation buffs such as Korzan's SP enhancement. If you can field a level 3 paradigm fire squad, you can even test this for yourself in the battle simulator.
    • Omni Paradigm Level 3 requires three 3 units, and two 1 units (or better). It also has to be entirely mono except for friend leads, so unless mono-fire becomes the meta (and it really needs a new mitigator for that to happen, at the very least), you won't be seeing this too much outside of FVA for now.

The takeaway from all of this is that Korzan getting up to 3 turns of 100% mitigation in arena modes is actually just the game's features, rather than a bug. And while Gumi could fix the extra turn from Omni Paradigm 3 if they wanted to, the extra turn enemy Korzan gets in arena can't be fixed without screwing up literally the rest of the game.

So have fun dealing with that.