Honestly I don't quite know, and only know that could potentially be an issue with a recent member of the server not having access to NSFW-marked channels and needing a solution. I believe you can do it directly through Discord but at this point I'm just guessing.
It sounds like it's a Discord-side problem though, so getting in contact with them might be the way to go? I'd be interested in knowing what the issue is and if there's anything I can do to help, but if it's not a ban then there's not really much else I can do.