2. Joseon Exorcist - controversy around use of Chinese props and cultural icons, food, etc. Show cancelled after 2 episodes aired.
Do cast scandals count? If so:
3. River Where the Moon Rises - bullying scandal involving Kim Ji Soo, gets replaced as ML by Na In Woo after first 6 or so episodes air. Scenes reshot with In Woo.
4. Hometown Cha-Cha-Cha - Accusations made by Kim Seon Ho's ex regarding how he treated her, abortion, etc. Short-lived after more info came to light and he had a lot of fan support. Didn't seem like it had huge lasting effects on him or the drama, but it was a brief controversy.