I think there are two potential ways to fix this apparent continuity issue regarding the Tantive IV receiving a physical copy of the plans or having it “beamed” onboard as Vader words it in ANH.

Honestly, a simple solution would be to remove the final two shots of Vader watching the Tantive IV undocking from the Rebel flagship. Not showing Vader see the Tantive IV might help alleviate the glaring obviousness of it clearly being a rebel ship and not a diplomatic one. Even though the Rogue One novelization says Vader notices the plans being handed off from rebel to rebel, I prefer to believe he was too focused on slaughtering them all to spot this trade off, which explains why he isn’t sure if the plans were beamed to the Tantive IV or the Rebel flagship or both. I can buy that, but seeing Vader sit there as Leia and Captain Antilles lie straight to his face about being a diplomatic ship when he literally just saw the ship flee the battlefield pushes it.

A more difficult solution would be to cut it in such a way that the person downloading the plans appears to be at the end of the hall, but instead, transmitting the plans to the Tantive IV. So Vader is charging down the hall to stop the plans from being transmitted. Maybe someone could generate a shot of the Tantive IV in the distance of the battle, or back and forth comm chatter between the two ships. The only issue would be explaining why soldiers wearing Alderaanian garb were on a Mon Calamari cruiser, and the coincidence that they just so happen to be transmitting to an Alderaanian ship.

This might be a hard change to make, and I’m okay with believing Antilles and Leia were playing with technicalities since no transmissions were actually beamed onto the ship, like Vader insisted. I think just not showing Vader actually see the Tantive IV would help this issue. But I’d be interested in seeing it if someone thought they could do it.