I have a .blend file used for animation which has a linked model/rig to a base .blend. This .blend file stores a bunch of actions and up until recently I've had no trouble using it to import animations for use in my game. But now, on Unity 2020.3.26f1 and using Blender 2.79a after having regenerated the Library folder (could be important for this) and made a build for 3 Platforms in a row, I've noticed that sometimes my animations get corrupt and freak out with random frames of nonsense movement. Take for example this animation in which the head glitches out upwards for a few frames before settling back: It does NOT happen at the loop point and is not due to rogue keyframes in Blender. As you can see in Blender, Frame 100 of this animation does not show the same glitch: The crazy thing is, this issue disappears once Unity re-imports it. All I've done is open and re-save the file in Blender and it's magically disappeared: To pre-answer common questions, this has happened before about a week or two ago with another one of my characters. The leg for that animation was glitching out downwards for a few frames before clearing up. At that time I solved it by re-saving and then also switching the anim. compression option to Keyframe Reduction rather than Optimal, just in case that was having an effect. Sadly I can't confirm if it fixes it since Optimal was the setting for this file I showed above. It shouldn't be affected by rotation/position/scale error since these jumps are way further than any error value, though in the past I have noticed some small shaky movements when these values were at default setting. The character is humanoid and I've already set up a custom mask to import all the bones that this character has. I can answer any questions you have about my setup. Seems similar to maybe this issue but otherwise I can't find anything like this online. The thing is this is easy to fix but hard to understand, and an overall scary bug to have. At any point it seems like any of my animations could be corrupted like this and although I can fix it just by saving the file, since there's no error report and the fact that this wasn't happening before, things like this could easily slip into the final release. In fact, this one made its way into the Beta release on my Steam app and it's the reason I found it in the first place. I have no idea how to even detect when this is happening other than manually looking through each animation and making sure they aren't corrupt. So this is starting to stress me out since I'm releasing this project in just a week or so. Appreciate any help and thank you for any guidance or info.