Would love some input on what I can do to correct this issue. Whenever the weight gets "heavy" I start jumping further and further backward - like close to 10-12" back. I don't see this happening at lighter weights at all, just when I start to approach heavy weights. This happens on both cleans and snatches but is most pronounced on snatches. Below are a few vids from yesterday. My PR is 80kg; these lifts are at 70 and 75, respectively.
You can try tall snatches. Put a thin mat behind your heels (give yourself an inch or two or space initially) and when you pull under, pick your feet up straight and plant them flat - heel and toe together. The knees cue means don't lift your feet by bending the knees, lift them by bending the hips (i.e. raising the knee) - this should help prevent you from sweeping your toes back out from under yourself.