Hmm, I don’t think you should leave the Apply Additive with no additive input like that, even for testing. There’s a node called ‘Apply Additive Identity Pose’ (or something like that) that you can connect to the Additive input which will basically feed it nothing.
As far as next steps, in addition to rebuilding your blueprint, I would look through your animation assets and make sure that only the anims that should be set to additive are. Also, on the ones that are additive, double-check that the additive base is correct and not an animation that’s on some other skeleton or something.
I have run into issues similar to this when retargeting anim assets from one skeleton to another. Everything would copy over and retarget great, but the additives would still be pointing to the Idle on the old skeleton.
Sorry for the trouble. I know weird bugs like this can drive you up the wall.