Is there usually a reason when a male member uses a club name like “X” (not their real club name)?

Thanks to Yazakura’s help, I figured it out. Apparently, if someone’s profile is set to public even though they haven’t configured it themselves, a temporary club name consisting of one character is assigned. Profiles are automatically made public unless the person takes action, so they may either be unaware that their profile exists or simply find it too much trouble to edit and leave it as is. It may also be because dating clubs originally operated on a system where men chose women, so there was no concept of male profiles to begin with—they were added later.

It might be YOSHIKI.