If God conceals a person's sin in this world and then that person repents of it, but after repentance their affair is exposed and they are reproached for it, does that indicate their disgrace on the Day of Resurrection, and how is this explained in light of sincere repentance?

Allah does not conceal a servant's sins in this world except that He will conceal them on the Day of Resurrection. Allah will bring the believer near on the Day of Resurrection and make him confess his sins, then He will say, "I concealed them for you in the world, and I forgive them for you today." This concealment is for the people of faith, not for the disbelievers and hypocrites. And a person being exposed in this world does not necessarily mean he will be exposed in the Hereafter, especially if he repents sincerely and conceals himself.