It was normals and smoothing options. Sorry man. For fbx it was 'tangents and binormals' For obj it was a combination of 'smoothing' and 'normals' with 'smoothing' off and 'normals' on, it seemed to fix it. i feel like such a big fool
SOLVED It was actually a bug, tested export again with all settings and the problem has just disappeared. I am awesome I guess LOL I keed. Christ. I really fucking hate myslef right now. I found the problem. I am sorry for wasting a thread. Tried exporting again with the problem child settings and problems disappeared now.…