Frozen could never quite justify the phenomenon caused by its hit song, “Let It Go” (the movie was a mid-tier Disney princess musical at best). That mediocrity is further exposed with Frozen II, a torturously convoluted extension of an already complicated narrative that can’t decide if it wants to be an origin story for snow queen Elsa, a romance for her sister Anna, a metaphor for living with grief and depression, or a parable about reparations due to indigineous peoples. (It takes on a lot.) The sister dynamic has always been the most unique thing about the Frozen story, but it mostly gets short shrift here, while the animation shifts between the dazzling (startling rock monsters) and perfunctory (a lot of the magic happens against plain black backgrounds). And the music? Kristen-Anderson Lopez and Robert Lopez return as songwriters, offering one number that tries to evoke the ice blast of “Let It Go” (“Into the Unknown,” also sung by Idina Menzel) and another, “Lost in the Woods,” that made me remember how much I detest Peter Cetera’s “Glory of Love.”