WARNING: The following contains spoilers for manga chapter #47 and anime episode 188 of Boruto: Naruto Next Generations.
In Chapter #47 of the Boruto manga, Koji Kashin makes a shocking face turn, backstabbing Jigen and his organization, Kara, to weaken the being possessing his body, Isshiki Otsutsuki. His goal was to ensure when the nearly-immortal alien's real form emerged that it would be vulnerable enough to defeat permanently. He worked with the terrorist cell's lead scientist, Amado, to this end. Their joint goal from the beginning was to sabotage Kara from the inside so that Isshiki Otsutsuki couldn't achieve his ultimate goals, which would otherwise doom the world.
However, as the anime dives into the Kawaki arc, which starts well before this betrayal happens, there are some clear signs of Koji's deception that Delta should have prepared for from the start. In Episode 188, Delta points out Koji's questionable actions to Jigen that delay Kara's mission and put its remaining Inners at risk. She takes umbrage at his insistence on retrieving Kawaki by himself before going on to hire Ao without anyone's approval. After the defeat of Inner members like Victor and Deepa, Delta expresses extreme distaste for Koji, who continually puts the organization at risk of further losses.
Delta also notes that Koji is the only one not being assessed by Amado. Instead, he avoids meetings entirely and is always on the move, yet never produces results. The audience realizes that this behavior pattern is a stalling tactic. Despite her suspicions, however, Delta never takes the initiative to investigate the matter herself. When she eventually gets the chance to have an audience with Jigen, she sees Koji monitoring Kawaki and Boruto instead of abducting them. Both have the Karma marks that Jigen needs to further his plans. When Delta eventually goes on a field mission to surveil him, he convinces her not to confront Team 7 and abduct the boys herself.
Despite this suspicious behavior pattern, Delta keeps accepting Koji's excuses when he should be urgently getting the Karma-marked boys back to Kara's headquarters. When Delta brings Garo with her to capture Kawaki, Koji lets the boy go with Konoha ninjas after killing the Outer. The masked man is evidently keeping Kawaki away from the organization's clutches, as he knows Jigen's most powerful form will emerge in him when the time is right. Koji was also the one who brought the airship down and freed Kawaki in the first place. Delta could have removed the double agent well before his actions posed a severe risk to their plans if she had reconciled all of this information with that incident.
The final and most evident sign of Koji's deceit is when he insists that Delta should not sneak into Konoha to retrieve the boys instead of leaving it to him. While Delta is still incredibly suspicious of him, she lets him go regardless. Koji's ability to effortlessly get past the village's sensory barriers should have been evidence enough that he was affiliated with Konoha, as no one else in Kara could have safely done so. However, in Chapter #47, when Koji finally defects from Kara to fight Isshiki in Jigen's body, Isshiki notes that he is a clone of Naruto Uzumaki's mentor, Jiraiya.
Delta is a character known for berating the people around her for not taking the best course of action. Still, in the anime, she has yet to take action on her justifiable suspicions that Koji is a traitor. Had she not waited for Jigen's approval or acted independently sooner, she could have disposed of Koji, gotten Kawaki home, and helped Kara reshape the world. Instead, Delta seems to bide her time when every second should count, considering how crucial Kawaki is to their plans.
