I've tried my own attempts at fixing the problematic VAE in SD, and I've even reverted to using 560K instead of 840K.

This VAE is far better than both of those options. The quality of this VAE feels like it was trained from the ground up on lossless PNGs instead of lossy JPGs.

It still has trouble spots in the exact same place as KL-F8, but I can't notice them unless I tweak the brightness or the contrast of the output image to insane levels.