The food replicator was already processing Earl Grey tea at the moment Picard said "Decaf".
When the Enterprise D is moving towards the camera to reveal Picard and Data through the hull windows, the window configuration and size of the room seen from the outside does not match the room they're sitting in when viewed from the inside.
Dahj's hair is or isn't tucked behind her right ear while sitting with Picard on the patio, depending on the camera angle.
For a sun to go supernova as the Romulan sun did, it had to be a lot bigger. Much bigger and larger stars only live for a few hundreds of millions of years, even less. No habitable planet can form near such stars If planets did form, they have no time to build up a life-enriched world. Even if the Vulcans were colonizing it in the past, it makes no sense to colonize a planet near a big star that would go supernova. The Vulcans/Romulans would have known this.
When Picard is playing cards with Data, it is obvious that Brent Spiner has gained weight since his days on Star Trek: The Next Generation (1987), which makes no sense for an android like Data. Since this scene takes place in Picard's imagination, it need not be strictly literal.
During the opening nightmare sequence, as the camera zooms in on Ten Forward, and Picard and Data playing poker, the camera zooms in through 3 narrow slotted windows. But, inside the room, they are playing in front of the more central windows, which have one wide window surrounded by two narrow slot windows. However, this could also be an indicator that this is indeed a dream, rather than an error.