ok so i was re watching the 2.8 trailer again just now and i noticed that when Ava and Anguis are having their conversation, when it skips back and Anguis is talking about "Will lead to... The Keyblade war" you can actually see Ava in the background.
This makes me think, that maybe Anguis has been caught out. Even her tone of voice gives off this vibe that she is giving this knowledge out regrettably. We do know that Ava seems to be one of the only foretellers who is actually trying to stop things from going horribly wrong.
After all, Anguis is the foreteller that we know the least about.
Just look at the body language and the tone of voice of Anguis and tell me what you think. She clearly knows something that she doesn't seem to want to divulge
Master Invi could be the traitor but she could also be not, we are more or less still in the phase where there are "bread crumbs" scattered around by the story that make alternately look a different Foreteller suspicious to the audience.
Like i.e. Aced's often openly hostile and more violent approach to things, Gula knowing some passages of the Lost Page itself or now this part with Invi.
There are also still other possibilities around, namely that there truly is no actual traitor and the whole thing is a setup to sow discord and turn them against each other, in the process one or more, possibly even all of them turning into an inadvertent traitor at different times.
The point with Ava is not exactly true as we have given hints about that at least Ira and Gula are at some points also trying to prevent things from getting worse.
We see Ira consult their Master on the issue in both of the latest trailers and he clearly intends to try and prevent things from going downhill.
I don't know if you've seen/followed the finale of Browser-Chi, but in the last update of the Browser game Master Gula (Leopardos) actually reveals to Skuld, Player and Chirithy that he did investigate into the traitor and tried to stop things but followed some wrong clues and ended up running out of time, things by then being irreversibly messed up causing him to give up.
Ava trying to stop things is just more obvious up to now because so far her actions are shown to the audience the most.
Every Foretellers knows something they don't want (or possibly don't dare) to divulge, that's because of the atmosphere of mistrust and discord that has been created between them. They are all anxious and afraid to reveal everything because they believe one of their number is a traitor and they don't know who can be trusted anymore, thus keeping things to themselves.
Gula even says "trust no one but myself" in the trailer, so while Invi hiding something might point to her as being the traitor, the other Foretellers are doing such as well.