There is no “one right” spelling of Korean names. Romanization standard keeps changing and no one can keep up with it. Sometimes it can be personal preference and other times, it’s written like that by an agency and I’m not talking about just the entertainment agency. So Seo Kang Joon could be spelled like Suh Kangjoon, Seo Kangjoon, Suh Gangjun, Seo Kang-jun, Suh Gang Jun, Kangjoon Suh, etc.
I’ve seen some Koreans in Korea using the hyphen in between the two characters of their first names, such as “Kang-Joon” but most Koreans who live overseas do not use hyphens.