Naju allegedly had access to an account with the check mark (Kiju's account), and apparently if you have one account with the check mark you also get the check mark on your other accounts. (Ik this doesn't explain why Naju doesn't have the check mark). Apparently Jesper and Jurgon knew this, but didn't ban him for it.
I heard that rumor on M8M6, but its pretty darn garbled and doesn't make much sense at all.
I also heard that Naju was on break due to school from another person.
I not sure anyone knows what's going on with him, but I hope this helps.