The last few chapters of One Piece have been going a little poorly for the Straw Hats and their new friends. Everyone's been trapped in the Labophase, communications are down, the Snail Cams are being taken out one by one, and the Seraphim are trying to kill everyone. Not to mention, this is all happening before Kizaru and Saturn have even arrived on the Future Island.
According to Shaka, there may be a traitor among the Vegapunks. It's difficult to understand why a Vegapunk would go full Benedict Arnold, but that leaves about seven suspects, including the Stella. Disregarding any possibilities involving Saturn or a secret eighth Vegapunk or some other undisclosed factor, here are the most likely suspects.
Which Vegapunks Are Least Likely to Be the Traitor?
The Seraphim are designed so that their orders cannot be overridden by someone of the same level of authority; they can only be handed new orders by someone on a higher level of authority or a lower level if the person who gave the order is rendered unconscious. Therefore, if one of the Vegapunks fails to make the Seraphim stop attacking, they can't be the traitor; this might change if it's revealed that the renegade Vegapunk was suicidal enough to order the Seraphim not to follow their next command, but that's yet to be revealed. For now, this is the best clue for readers to go off of.
So far, a few Vegapunk Satellites have been shown trying and failing to rein in the Seraphim. Lilith and Shaka explicitly tried and failed to order them to stop, so they were cleared of suspicion. Pythagoras also reportedly failed to order S-Snake to stop, though he wasn't shown doing this. York also mentioned Edison's orders to S-Snake before she was petrified, though this could be seen as more of a review of the facts than a direct order. Ideally, this should mean that all four of these Satellites are cleared of suspicion.
Unfortunately, Pythagoras and York's stories still don't completely check out. While it's true they were both attacked, this could have been part of the plan. Either of them could have secretly ordered S-Snake to attack or even "eliminate" them so nobody would suspect them; Pythagoras could "luckily survive" with just his head and York can be unpetrified after everyone else is dead. As the first two Satellites to be attacked, they're also among the most suspicious.
Atlas is mostly clear of blame, but not because of any interaction with the Seraphim. She was being repaired when the Frontier Dome defense system shut off in Chapter 1071, "The Hero Deploys." She might have snuck off to shut these defenses off when no one was looking, but she at least has this alibi for what it's worth.
Which Vegapunks Are Most Likely to Be the Traitor?
As hard to believe as it is, the main Vegapunk is one of the most likely to have set all of this up. He, too, was notably unaccounted for when the Frontier Dome was shut down; he was later found by Jewelry Bonney, who happened to be running around the lab interior looking for him. He also went missing altogether around the time the Labophase was sealed off; wherever he's vanished to, he has some explaining to do once he's found. However, he's still not the Vegapunk fans are most suspicious of.
Of the seven Vegapunks, Edison is the most suspicious. He, too, was absent when the Frontier Dome was turned off and possibly when control was lost; while attention has been drawn to the fact that the Stella has been missing in these events, Edison is equally suspicious. He was also the last one to give the Seraphim an order, so he should still be the one in charge; again, his being attacked might have been part of the plan. It's not a lot to go on, but it's more than most of the other Vegapunks.
As for why Edison would do any of this, that remains to be seen. Some things that could clear this up would be seeing more Vegapunks getting attacked, the location of the Stella, or simply some more information about either the Vegapunks or the Seraphim. Until then, Edison is the safest bet as the traitor.