2. Goblin: When Kim Shin (played by Gong Yoo) is afraid of the movie Train to Busan, even though the actor plays the main role in the movie
3. The Legend of Shen Li: MLs ears were red whenever they had to film more intimate scenes which was a running gag for the crew as well as the community
(Sorry, I'm not sure if that's what you meant, it‘s more like inside jokes, I guess. ..#2 isn't really a running gag, just a one-time thing and #3 is more like a behind the scenes thing..but I can't think of anything else right now...if it doesn’t fit, I can delete it again)