Short answers to the questions that come up most. Each one links to the full version.
Usually one of three things: a Relax/Autopilot score under 75% accuracy, a Flashlight score with non-default settings, or a mod that does not earn pp. Full list on the Scoring & pp page. The score still submitted and still ranks by total score, it just gave no pp.
No, it is not broken. Those boards only show scores from your friends, or from your country, so an empty one just means nobody in that group has set a score on that map yet.
Yes. On Torii, unranked, graveyard and loved maps give pp and have leaderboards. On official osu! standard those give no pp at all, so this is a real difference.
Yes, both are fully ranked here, each with its own leaderboards.
Yes. Custom rate variants of DT, NC, HT, DC and Easy still earn pp on Torii, unlike official osu!.
No. Nothing on Torii auto-bans you and no score is auto-rejected. Every restriction is a manual staff decision. See Restrictions & Appeals.
Open a ticket in the Discord and wait about a month before appealing. Details on the Restrictions & Appeals page.
Report it in Discord instead of farming it. Because unranked maps give pp here, a broken map can hand out absurd pp, and knowingly farming one without reporting it is bannable.