Their personalities just don't mesh well together. There's also the fact that actor Sejin has a hard time talking about his issues even when they may affect the team (like with his previously signed company and another that will come to light).
Then, on big Sejin's side, he is desperate to keep Testar afloat because he's been a trainee for too long (he develops an inferiority complex towards much more talented idols) and doesn't like that the other Sejin clams up about himself with his scandals. Fortunately, they eventually put aside their differences and find a middle ground in the latter half of the story.
thats nice to know, thanks
bound to happened since in the group they have the most incompatible personality basically Lee Sejin and Bae Sejin have different entire personality especially when they did an mbti test. for reference Lee Sejin is an ENTJ while Bae Sejin i am ISFP, they don't have any match personalities at all.
are sejins having beef?