WARNING: The following contains spoilers for Star Wars #10 by Charles Soule, Jan Bazaldua, Rachel Rosenberg, and VC’s Clayton Cowles, on sale now.
Marvel's Star Wars comic has detailed Lando Calrissian's heroic turn after The Empire Strikes Back as he attempts to redeem himself for betraying Han Solo and turning him over to Darth Vader and Boba Fett. It informs how he officially joined the rebels before The Return of the Jedi, working with Leia and manning the Millennium Falcon with Chewbacca to atone for his sins.
However, Star Wars #10 apparently reveals tat Lando was still a traitor during this rehabilitation period, working under the thumb of Jabba the Hutt.
By this time, Lando was running point for the Fourth Division, helping the Rebel fleet as Leia tries to find a new way to send coded messages out. He worked with Poe Dameron's dad, Kes, to steal a droid that can encrypt the messages so the Imperials can't decipher them, but they're struggling to get the bot to work. That is, they have trouble until Lobot locks in and allows it to process the info, with Lando threatening the Talky droid with death.
But as he leaves the room, his comms unit buzzes, and it's Jabba's right-hand man, Bib Fortuna, calling in. He makes it clear they still own Lando, despite the Han deal, and that they need info about the Rebels' activities. They want to sell it to the Empire, with a finder's fee for Lando. Surprisingly, rather than lie, Lando tells the Rebels exactly what they're doing, endangering Leia's mission big time. He cuts the call short to not get detected, which makes it uncleaf if Jabba will sell this info or wait for more juicy details from him.
It's also not clear why Lando is still working with them if he truly wants redemption. Assuming that Lando isn't serving as a double-agent and playing Jabba, they could have something over his head we're not privy to. In all likelihood, Lando is most likely playing them like this to help him get closer to Han's rescue, but it's still not smart leaking this bit of intel. It's giving the enemies the ultimate heads-up, and it's not hard to see why Lando is keeping this secret from the other leaders of the Rebel Alliance, especially after the death of Needle.
For the moment, Leia is out of ideas, and Lando has seemingly betrayed her trust, to some extent at least. While Lando has always been a self-serving character, this crosses a line, even for him. Still, we know he eventually helps them recover Han and battle the Empire, so his true endgame here remains unclear, even if it's bringing Darth Vader closer and closer to them.