Creality Ender-3 V3 KE & SE machines with extreme bed levelling values and large variations can be caused from incorrect standoff locations holding the hotbed.
The bed used on both Creality Ender-3 V3 KE and SE machines is held with 4 plastic standoffs, of which two are longer than the other two. The height difference is less than a centimeter, but more than enough to skew to the buildplate and make it difficult to impossible when leveling. Here is a diagram of where they must go:
Essentially the two short standoffs (approximately 14mm) should be placed on the left corners of the bed, the remaining two long standoffs (approximately 16mm long) should be on the right corners.
You can also print a new one using this downloadable 3d model:
https://www.printables.com/model/762799-ender-3-v3-ke-bed-spacers