The first “Pitch Perfect” was no great shakes, but though silly the “Glee”-ful musicomedy about a girls’ collegiate a capella group had a dumb affability that audiences appreciated. Its success made a sequel inevitable; a pity it couldn’t have been better than this.

As “Pitch 2” opens, the Barden Bellas—now led by Chloe (Brittany Snow)—are three-time national champions (a premise that stretches credulity, given their quality), chosen to appear at President Obama’s birthday bash at Lincoln Center (even more implausible). During their routine, Fat Amy (Rebel Wilson), who’s for some reason being lowered from the rafters, slips off her perch and has a “wardrobe malfunction” of a particularly revealing kind that the media soon dub “Muffgate.” In reaction to the scandal, the college forbids them from recruiting new members and the national A Capella League strips them of their worldwide tour duties, handing the gig over to the arrogant, spit-and-polish German group Das Sound Machine headed by the Kommissar (Birgitte Hjort Sorensen) and Pieter (Flula Borg).

The disaster obviously sends Chloe, as well as teammates Amy, Cynthia Rose (Ester Dean), Lilly (Hana Mae Lee), Stacie (Alexis Knapp), Jessica (Kelley Jakle) and Ashley (Shelley Regner) and newcomer Flo (Chrissie Fit), into a tizzy. Beca (Anna Kendrick) is none too happy about it either, though unlike her singing pals, who seem oblivious to actually preparing for life after graduation, she’s secretly arranged for an internship with a high-octane record producer (Keegan-Michael Key) and is anyway spending time with her beau from the Treblemakers, Jesse (Skylar Astin).

The Bellas are determined, of course, to win back their reputation in the only way left to them—beating the Germans in the World Championship at Copenhagen. Their efforts to rehearse, however, are undercut by Beca’s work at the record company, and by the efforts of Treblemaker Bumper (Adam DeVine) to court Fat Amy. Further trouble comes in the form of freshman Emily (Hailee Steinfeld), whom despite the dean’s ban they welcome into their club as a legacy member (her mother being a legendary alumna played by Katey Sagal), and who seems intent on inserting original material into their routines. (She gets a suitor too, in Jesse’s pal Benji, played by Ben Platt.) Things go particularly badly at a rural retreat run by their old leader Aubrey (Anna Camp).

The major problem with “Pitch 2” is that the central narrative thread, involving the resurrection of the Bellas’ reputation, is poorly played out. Their “comeback” routines, in which various catastrophes occur (like Cynthia-Rose’s hair being set afire), aren’t just clumsy but unfunny, and so is the sequence set at Aubrey’s resort, where slapstick reigns. Especially bad is an unofficial a capella face-off staged by a creepy fan played by the equally creepy David Cross (and featuring some Green Bay Packer players as unlikely singers). And all the spoken material featuring the Germans is dreadful, like outtakes from a bad Sprockets sketch from SNL.

It certainly doesn’t help that neither Kendrick nor Wilson carries the movie the way they might be expected to do. Kendrick looks dour throughout—she looks as if the sequel was a contractual obligation she would have preferred to have passed on—while Wilson does her usual shtick, which this time around just falls flat: most of her muttered asides lack snap, and frankly seem as though they were separately shot and just edited into the mix later. As for Steinfeld, who’s obviously on hand to serve as the linchpin for any further sequels (the current crop of Bellas suddenly deciding to graduate at the close, though none is ever seen going to class or cracking a book), she’s basically a cipher.

Still, though the movie is vacuous at the core, there are occasional redeeming moments. Though his material isn’t first-rate, Key invigorates every scene he’s in, and a cameo featuring Snoop Dog is especially good (though it’s spoiled by a Kendrick-centered resolution). The commentary by returning “on air” oafs John Michael Higgins and Elizabeth Banks (who also directs, without distinction) has a few barbs (especially Higgins’ obliviously insensitive remarks) that are almost worthy of Christopher Guest. Platt’s nervous bumbling has some charm, and Fit’s darkly comic interjections about her Guatemalan upbringing hit the mark. And Wilson finally gets the chance to shine when she romances her would-be boyfriend with a lakeside rendition of “We Belong” late in the game—the awkward amateurishness of delivery is still there, but the idea is good enough to overcome it.

And, of course, there is the music, which, though occasionally underscored with instruments in violation of a capella rules, some viewers will enjoy. (Perhaps the best joke occurs at the very start, when a group does the Universal Pictures intro music in the style of the Swingle Singers.) The technical side of things is decently handled, with the cinematography (Jim, Denault) and production design (Toby Corbett) showing the effect of a larger budget than the original possessed.

But overall “Pitch Perfect 2” feels tired and off-key, a bungled attempt to recapture the modest charms of its overrated predecessor.