In a romantic comedy, any good-looking British actor can probably coast along on his charm and accent and manners. But to do what Hugh Grant did in the ’90s — to make you believe that for all his cultivation and civilized sex appeal, he lives inside a spectacular thicket of self-doubt that’s even more enchanting than pure confidence…well, that takes a true actor, and maybe a star. And that’s the quality Sam Claflin has in the minor but captivating “Love Wedding Repeat.” He plays Jack, who spends his sister’s wedding trying to put out a dozen fires at once. To say that the character is working overtime to hold himself together would be an understatement. He’s exquisitely flummoxed.

At the outset we hear a narrator, who sounds like the ribald version of a “Masterpiece Theatre” host, as she offers up cynical bites of wisdom like “One bit of bad luck,...