The heterosexual rapture of Abdellatif Kechiche goes on … and on … and on ... and on. His epic female buttock fetish stretches to the far horizon. Kechiche has reaccentuated buttocks. He has doubled down on buttocks. Almost the very first shot is of a woman’s naked bottom, massively filling the screen, like an inflatable by Terry Gilliam.

Mektoub My Love: Intermezzo is a bizarre, colossally self-indulgent, almost avant-garde followup to the Franco-Tunisian director’s previous film Mektoub My Love: Canto Uno, whose combination of hedonist 90s nostalgia with scenes of cinephile brooding on silent cinema and patient photography of farmyard animals made it, for me, a good and interesting film – and I stand by my response to that specific work. But it had its detractors, who found it nothing more than pornified leering and hateful misogyny – an example of the toxic male gaze, though accusations of the white gaze will have to be directed elsewhere, and Kechiche has always had a sharp, sympathetic eye for the North African communities in Sète, in the south of France, where it was filmed.

Well, Mektoub My Love: Intermezzo must surely be the most purely experimental film to be shown at this year’s Cannes film festival. It shreds the rulebook about narrative and character development. In this monumental photolove-smutfest, what happens – actually, the word “happens” is misleading in this context – is that Amin (Shaïn Boumedine), the shy student from the first film, is still hanging around his hometown and obsessing about Ophélie (Ophélie Bau), who has been having an affair with Tony (Salim Kechiouche) while engaged to a guy called Clément who is off doing his military service, and is basically the Godot of the Mektoub franchise. But Ophélie has a secret, which she confides to Amin and asks him to help with.

There’s a scene on the beach, and then a scene in a nightclub, which in a normal film might take together around 10 minutes before the story would properly get going. Here these two scenes take up the entire film, and the nightclub sequence itself occupies a staggering three hours running time, interrupted by a full-on sex scene in the toilet: that, in fact, is the real “intermezzo”. And what is so extraordinary is that after three and a half hours, there are still untied plot strands. Another movie like this could be in the offing. And yet this one feels as if Kechiche has simply given us three-and-a-half hours of his unused beach and nightclub footage from the first film.

So I have to admit it: Mektoub My Love: Intermezzo defeated me. Kechiche is starting to look less like Eric Rohmer and more like Russ Meyer. It is as if Kechiche is repeating the classic question once posed by Spinal Tap’s Nigel Tufnel: what’s wrong with being sexy? All the interesting parts of the first film, all the things that gave it perspective, have been amputated, leaving us nothing but some sort of arthouse Love Island. And the emotional blankness of the characters in that endless nightclub scene, always laughing and dancing as if they have had a very strong MDMA pill – or a lobotomy – is just plain weird. It seems as though all this dancing must surely lead to something: some outbreak of jealousy, or toxic male aggression, or maybe some Stepford revelation. But no. Nothing.

Of course, it is conceivable that this frantic dancing makes sense for Ophélie, in that she is trying to distract herself from the reality of her failed relationship and what she must now do to keep her affair secret. But Bau’s performance never really conveys any of this. She just looks sexily placid and placidly sexy.

For all this, Mektoub My Love: Intermezzo is clearly the work of a serious film-maker, and that toilet sex scene with Ophélie delivers a wood-splintering punch. Inevitably, as with all sex scenes, there will be people who will airily claim that this scene is “boring”. It isn’t boring, and people who say this are suffering from Pinocchio-nasal syndrome. But where does it lead? Nowhere. Afterwards, we are back in the nightclub, nothing has changed, and Ophélie’s choice of partner is something else that is unexplained and unsatisfactory in dramatic and psychological terms.

Kechiche is a brilliant film-maker and a deserved Cannes Palme d’Or laureate for Blue Is the Warmest Colour in 2013, when he won jointly with its stars Adèle Exarchopoulos and Léa Seydoux. Of course it is possible that, after another four-hour film, the shape and meaning of the whole Mektoub trilogy will become clear, but it’s doubtful. The project is starting to look worryingly like some sort of midlife crisis.