Keyframe corruption and duplicate teleportation

Sorry for the cryptic title but I have no idea how else to describe it as I have an animation project of a little over 500 frames and the longer it goes on the more problems I encounter. My workflow is to set the start and end frames of my timeline to break up the animation into manageable chunks as the camera jumps on the end of each of these segments to a new static position.

I started noticing this problem today whereby the character would normally make a subtle gesture but there is a new key frame that I know was not there before and the arm IK control shoots off to a duplicate position that it supposed to be later in the animation as I am working non-linearly to block out the biggest bits. I thought this was a mistake on my part but they kept showing up more and more frequently. Duplicate keframes from later in the animation suddenly appearing earlier in the timeline, utterly messing up my animation. Deleting them seems to solve the problem but just as I think I have solved that issue I start scrubbing the timeline outside the bounds of the of the start and end frames of the chunks that I am working on and discover another problem having appeared at the same time!

The newly discovered problem sees preexisting keyframes having completely random position, rotation, and scale values so that my characters are freaking jumping all over the screen!!! It gets even stranger, because I keep creating new and redundant saves to avoid problems like this, but save files that I know, I KNOW to have been just fine before have the exact same problems in the exact same places!

HOW DOES THAT HAPPEN?!

Does anyone know what is happening, how to fix it, and how to avoid it in the future? I am utterly livid over all the work I have lost because of older saves all having been somehow corrupted by this problem.

P.S. I am using this rig right here: https://flippednormals.com/downloads/base-meshes-character-starter-kit-rig/

Thanks for any advice you can offer!

EDIT: I forgot to add that the corrupted key-frames only have random values in the pre-existing vectors and rotations that they already had; Say, a cube is keyframed being moved in the Z axis it will have only a randomized value in the Z axis and no added rotation values or shoot off in the X or Y axis.

Never noticed something like that. Sounds more like a rig problem to me. Download a free rig and try to replicate that behaviour.