I'm in the following channel # and it's not displaying in the /LIST.

I think this is mIRC related problem as in HexChat I do see the # in the /LIST.

Go to the /list window, right click and select "List options". There should be an option checked "Hide non-text channels", uncheck it.

This should fix that issue.

Wow, thanks alot! Idk why I never noticed it in all those years :P

You're welcome!

I do think it's a bit silly that this setting seems to be checked by default, however, I do not think it matters enough to be changed since the option is just a simple uncheck.