Timeskip. It's common thing. His hair's long because there has been a lot of time between the two events as was stated explicitly in the chapter. Also, his previous team members, excluding Silence, died to the invisible Ellous bc they got too cocky.
+ additionally, the Omega Squad are only reserved for emergencies since they're filled with "criminals" (as in they're the generation of Psykers that had to be killed off because they went out of control and bloodthirsty). They're probably locked up somewhere.
Ah okaayy! Thanks for explaining!
I don't understand. What happened to the group that helped Lee Han's group in chapter 90? how come Lee Han has long hair now? It feels like there are a couple of chapters missing between chapter 90 and 91.