The reason people compare this to Kaufman

No, I don't think it's a Kaufman rip-off as a whole, the tone is definitely different. But it is undeniable certain ideas and scenes are derivative of Charlie Kaufman's cinematic language, borrowing his ideas here and there and inverting them from a different point of view.

Here's what I mean by Kaufman's language. It is characteristic of the blurring of the internal and the external, such as the technique of visualizing memories, subconsciousness and other abstract ideas as literal set pieces. Now clearly, Kaufman did not invent this, David Lynch had already begun playing with dream logic, abstraction and internal landscapes since Eraserhead. What makes Kaufman an original is that he is one of the first screenwriters to deconstruct the conflict between the internal and external, to lay bare the mechanisms behind the never-ending struggle of being a character on the world's stage through characters in a film medium. His films reconcile seemingly paradoxical states and ideas within a coherent narrative. They are completely self-referential yet at the same time diegetic, maintaining their own internal logic while at the same time referencing themselves to mimic the human state of self-awareness and self-consciousness. This is strictly Kaufman's territory, and it is inevitable that anyone attempting to do something similar will be compared to Kaufman unless they find their own way to do it.

Now Sophie Barthes is NOTHING like Kaufman in these respects. Cold Souls is plotted in a straightforward manner, the only self-referential element being a deviation that proves the rule: Having Paul Giammati play himself. This is, IMO, unnecessary to her overall approach to tackling the existential theme and ends up being a distraction to other more effective moments in the film. (It also, as some critics have noted, bring up surface comparisons to Being John Malkovich, obviously an influence to Barthes.) The subtext would have been the same even if she hadn't broken the fourth wall with a fiction character.

This is where the 'rip-off' accusations come from: her approaches to depicting the existential crisis are centered around concepts developed by Kaufman. All the people denying its resemblance to Kaufman's work will do well to watch the scene in being John Malkovich where characters crawl through John Malkovich's subconscious and the scene here in which Paul Giamatti's characters looks at his soul. (A similar scene is to be found in eternal sunshine of a spotless mind.) The idea of someone buying a celebrity's soul for use is the literal inversion of John Malkovich being exploited as some kind of carnival ride. This comparison makes sense... While BJM was about control, Cold Souls is more about identity and what it means to be a person. The "soul fragments" idea seems to be developed as an afterthought to certain unanswered questions from BJM, in which people all coexist in a person's body through a portal. The idea of a partner feeling a different person inside of you in bed is also taken from Kaufman.

Barthes is a director interested in some of the themes Kaufman is also interested in, but hasn't found the most original route to express her vision. Personally, I feel she has an anemic approach to depicting existential crisis. The direction in this movie was beautiful, but the script was pretty lackluster and the idea of a soul was dead on arrival barely explored as it developed. Still it has its nuances, which would suggest Barthes would do well with a more subtle script about existentialism. She works on a palette more limited than Kaufman, and she could work this to her advantage.