Got a raid from them too. My base is near the swamp below Squin, raids started whem my scouts reached northern coast hive and travelled to Sho-Battai. Some weird trigger there, didn't fight anyone, -100 Yabuta rep, warleader says I imprisoned someone. I'm using Kaizo with UWE's compatibility patch, just in case.

Same here. Built a small outpost in the Cannibal Plains to serve as a base for my anti-cannibal crusade, next thing I know, I have a Yabuta Outlaw raid with several dozen 70+ stat outlaws out for my blood.
Managed to survive with heavy losses to my team. I try to follow them back to wherever their base is and I find out that their base in Darkfinger (or thereabouts, I dotn remember the exact place) is still a placeholder because Yabuta hasnt even been freed from prison yet.

Built a base in the fog islands and constantly got raided by these guys like every 12 days, until recently where my last raid in like 2 weeks was just Gurglers with no mention of upcoming Yabuta Outlaw raids. I think the trigger is just finding the abandoned Yabuta camp. I was additionally raided by the Outlaw Farmers despite being like half a map away. I was thinking these two factions hated me for allying with the UC [through bounties], though I'd be surprised if all 4 of us did that.

Since they have late game stats, it might be worth visiting the location on purpose to trigger raids for combat xp. Good armor and hiding food (I think bandits don't steal from bags?) should be enough to survive. The chiefs have stats in the low 70s, which makes them ideal for the Prisoner Recruitment mod. Otherwise, they are like 20k paying bounties to turn into the Holy Nation/United Cities. The regular dudes sometimes have a bounty of around 3k but only for the UC I think.

This should now be addressed, as of the version 30 update. Feel free to report if you are effected otherwise though.