I already had a theory but thinking all over it cames to an general discussion so here are my resluts:
First we have to think about that not only things that happens in LD are locating the traitor. FA and MoA are also involved. Another big point is the motive of the traitor. Nobody wakes up in the morning thinking "Oh lets betray everyone"! The last thing we have to think about is the opportunity to betray the Sunrider. Note: Ava says something important: PACT was warned since operation wedding crash!
On this thoughts i get started:
1. Opportunity - based on Avas theory the traitor has informed PACT since operation wedding Crash:
AsagaAvaChigaraCosette - wasn't on the Ship at the time of "wedding crash"
ClaudeIcariKryska - wasn't on the Ship at the time of "wedding crash"
SolaSo Kryska nad Cosette are out of the Game - they weren't on the ship and could'nt warn PACT about the upcoming operation. There is also the point Asaga could'nt warn PACT - she told them not to get after her but at this point this could be a plan leading them into the trap.
2. Motive:Asaga - The motive all are thinking about is her turn to evil because of the Sharr. But this just begins in the end of MoA! before this time she is getting jealous about Chigara and Kayto but there is no general motive to betray the Sunrider and cooperatre with PACT. She doesn't have a general motive.
Ava - There is not an single sign why she should have a motive to betray Cera and support PACT. When she is the traitor she must have cooperate with PACT since the begining of FA. I can't see a reason why she should help to destroy her home and murder civilians. Also she is totaly in order and paperwork. Rules are her highest pleasure. She wants to execute the ceran Soildiers who cooperate with the Pirates in MoA. I can't see a motive.
Chigara - She could have a motive. Being an Prototype would be enough already. But there are so much doubtful details wich doesn't make the situation clear. She could destroy the Sunrider serveral times and end it all. But she doesn't. But she has the knowledge and opportunity to contact PACT without being caught. The relationship with Kayto could also be real and fake. It's hard to think what's behind the mask of Chigara. Is she pure or is she the traitor? There is also a parallel to Sunrider: Academy where she had an twin sister Lynn. They swaped roles in her route so an fraud of Chigara could also be an fraud of Lynn as Chigara - why not? Against this theory ist my former Post. The argument in it make it be a little more complicatet... But Chigara could be the traitor on this point...
I don't really want anyone to be the traitor but here are my thoughts about that topic: WARNING!!
deep spoiler...
Spoiler
I think there ist one detail in the new beta wich made me think about it. Alice talks with an unknown Voice wich has warned PACT. She calls the voice "traveler". If this is an hint to the traitor (and i think so) then there are not many Girls wich can be it. For my thoughts it could be Sola. Why? She ist the one wich fits the term "traveler" most. It haven't be the Sola wich is on the Sunrider but one of her other
personalities in another dimenson. In Solas path in Sunrider Academy this subject was the main plot. It could be that one of Solas personalities came to this Universe and support PACT to defeat the Alliance an rebuild the Ryuvian Empire. She were the Sharr and want to be it again. This motive is also fitting for the actual Sola. So why not?
On the other Side Claude can also named as traveler. She traveld a lot before hireing on the Sunrider didn't she? But I cannot really think about a plausible motive for her. Asaga and Chigara are too obviously for me and it qould disappoint me a lot when there is no good plot twist in the end. We'll see.
But if i had a whish it would none of them. Then the traitor would be an alternative personalitie of Kayto...

Claude - Claude is an unkown character for me. I cannot imagine if the is only a little pervert doctor or an traitor. She could have the opportunity to betray all but what's about the motive? This would be very theoretical but none very good sign is seen in FA,MoA or LD so far why she could be the traitor. But maybe there'll comes an motive in the final part of LD.
Icari - Also an more or less unkown character for me. But she could have an motive. If she never gave up the hate on PACT and is in favor for an war of extermination against PACT there is an chance to be the traitor. First she wants PACT to dominate the neutral Rim and attack the Alliance after the war happend she doesn't want a freedom. She wants death to PACT so the must go on. I know the motive isn't strong but it could be an alternative.
Sola - Sola... In my opinion the bigest candidate for being the traitor... why? There ist so much mystery around her. First she is the formal Sharr 2000 years ago - but did sleep only 3 month in stasis like claude found out? She is also focused on the Ryuvian Empire and supports Asaga as her queen in LD so far. She also doesn't argue with Asaga when she has the chance - she let the sharr get stronger and stronger. Maybe she wants Asage to be going mad? But why should she support PACT? Well there are serveral theorys. First of all PACT could found Solas body first. As we know from the Prototypes they are able to clone. We also know from Sunrider: Academy that Sola is divided in mere realitys wich are bound to her yet. This could be a result of an DNA experiment with her. PACT took Sola with them manipulated her an put her back in her place where she is wating for someone important. But how could they plan to put her on the Sunrider? They couldn't. But they could wait for an Ship wich is in their interest and let her find Sola. If the Ship would be useless it would be destoyed by the System. If the Sunrider was an importand Ship at this time to PACT or not cannot be answerd. The theory is also very vague - too much unknown quantity.
The general motive of Sola could be the rebuild of the Ryuvian Empire and PACT is an force wich could help her to do so. Ryuvian was an powerful and maybe also cruel empire in her times. This is what she is telling us. Also she is only an "half Sharr" - but why? She also says that the sharr is the result of DNA manipulation wich is only made in the Royal family. She has an common mother but why should they only manipulate her half? It dosen't make sense to me so far. This and that she only spend three month in her tank make me suspiciously. There is something hitten. Another hint ist the FAQ from the Sunrider: Liberation Day webside. There is one question:
Mask of Arcadius says that the next installment was going to be called Rebirth of the Holy Empire. Answer: Once you play Liberation Day, you might just be able to find a surprise.
It could be an hint of trying to rebuild the Holy Empire of Ryuvian. But is the person who wants this most Sola? Why not!
3. ConclusionIn the end there are four possible candidates for being the traitor with the possibility i think so far:
Chigara: 70%
Claude: 55%
Ikari: 30%
Sola: 89%
I think Chigara would be like Asaga too obviously and would disappoint me a lot. I hope for an big bang in the final and a traitor wich is not be mentioned so far. I think there are some points i forgot or that will be come to my mind later i'll add them in the discussion by time.
But for now: Merry Christmas everybody!!
