What is it with the Duplass brothers? The conjoined architects of the mumblecore genre, Jay and Mark Duplass (The Puffy Chair, Hump Day) have now created two multiplex films, 2010’s wonderful Cyrus, and this year’s less wonderful Jeff, Who Lives at Home, both centered on old-enough-to-know-better boy-men still living at home with their mothers.

Cyrus milked that slightly icky scenario for skin-crawling comedy, as the title character played by Jonah Hill keeps nudging his porky, sad-eyed self in between sexy mom Marisa Tomei and her new flame John C. Reilly. At least Hill’s character had something akin to ambition in his pipe dream of a musical career — delusional though it might have been. But this film’s 30-year-old Jeff (Jason Segel) has no such aspiration. He’s content to camp out in mom Sharon’s (Susan Sarandon) Baton Rouge basement smoking pot and watching daytime television. Guided by the zen of Netflix and the world-according-to-M. Night Shyamalan, he sees the oft-viewed Signs as the key to the universe.

The perpetually stoned Jeff’s mojo kicks in when he gets a “random” phone call that promises to jumpstart his destiny. “What if there’s no wrong numbers?” Jeff wonders after an anonymous caller rings for “Kevin.” Jeff embarks on a crosstown journey, following myriad clues in search of the mysterious Kevin. Fate, the Duplass brothers suggest, works in mysterious ways as Jeff plays pickup basketball on the wrong side of town, runs into his brother Pat (Ed Helms), and follows a candy truck called Kevin Kandy on a circuitous journey to discover his purpose.

Like Kevin Smith gone metaphysical, Jeff, Who Lives At Home is slacker philosophy 101, finding poignancy and poetry in the random connections Jeff makes between not only the strangers he meets, but his own brother Pat, as his own path eventually — prophetically, Jeff would call it — crosses with Jeff’s. Equally stunted but more high-functioning, Pat is a skeevy middle-management type with a scrupulously manicured goatee and delusions of grandeur. He takes business lunches at Hooters and is convinced life owes him a Porsche, rental apartment and disapproving wife be damned. “This is going to solve a lot of our problems,” says Pat, breaking the news to his wife Linda (Judy Greer) that he has bought a Boxster without her knowledge. The estranged brothers have proven major disappointments to their middle-aged office-slave mother Sharon, whose sexually flatlined life is jump-started by an anonymous office admirer. The entire family is stuck in an existential rut, which the screenplay hints may be linked to the death of Jeff and Pat’s father.

There is a semisweet center, but also an overarching formlessness and meandering dopiness to Jeff, Who Lives at Home that makes the film far too thin and emotionally threadbare for feature length. Jeff and Pat play comic types: the slacker deadbeat son (albeit a lovably goofy performance from Segel) and the uptight, clueless brother. Far more interesting is Sarandon, who plays her unhappy mother as something more human and real. The mother and her sons seem to occupy two different realities: theirs cartoonish and exaggerated, hers melancholy and rooted in a loneliness she makes palpable. Sarandon feels like an actual person trapped in an attenuated comic skit that’s gone on for far too long.

Still, there is something purposeful and tender in the connections the brothers Duplass are trying to repair between the generations of parents and children in their films, even when they feel half-baked. While Pat trails the wife he suspects of cheating on him, Jeff follows clues that ultimately lead to the film’s message: We are all connected. After an act of heroism, the family reunites, and the film concludes in a happy, golden haze of togetherness restored.