Reporter Kjersti Flaa uploaded footage from her 2016 sit-down with Blake to promote "Cafe Society" ... and the journalist blasted their chat as her "most uncomfortable interview situation" ever.

Watch the vid ... there's tension right out of the gate when Kjersti congratulates Blake on her baby bump -- the actress was pregnant with her 2nd daughter, Inez, at the time.

Blake definitely was not thrilled to have her pregnancy pointed out, because she immediately hit back with. "Congrats on your little bump."

We should note, Kjersti was not pregnant.

The awkwardness only grows when the reporter tries to pivot to discussing the film's wardrobe ... with Blake icing out the interviewer altogether and choosing to only address her costar, Parker Posey, who was sitting next to her.

The drama comes to a head when Blake makes a dig about people thinking they know celebrities personally, calling out the media for being "intrusive."

Now, let's be real ... Kjersti's reposting the video, because of all the buzz around Blake's beef with her "It Ends With Us" costar/director.

TMZ broke the story ... a big part of their drama stems from Blake feeling fat-shamed by Justin during production, because he asked the film's personal trainer about Blake's weight in preparation for a scene where he had to lift her.

As we reported, Justin was asking because he's had back issues -- not because he was calling her fat, but that clearly wasn't how it was communicated to Blake.