Today i tried to resolve this problem, but currently i didn't find any good solution.
What i can say so far is that the game engine itself switches for NPCs the idle animation any time the current animation ends and randomly chooses another one from the same category, like sitting or standing.
For the player there is only one animation per category by default, so that one entry for those in an OAR submod is enough (eg. '_variant_mt_idle' folder). For NPCs it's required to replace any available entry, which could be a lot, sometime more then 10 different idles, like standing and wipe brows. So i tried to link or copy the additional required folders to the main submod folder and that part works, but the animations are still switching like you said. I don't know if there is a chance to configure OAR in a way that it keeps the current animation running.
To stop the animations from switching the behaviour graph must be modified by an esp mod file afaik, but that doesn't make sense for an OAR mod.
