2019 D LMC Struck Through Grease With Questions

Some of what you are seeing is called rolling lines. The lines formed on the stock material when it was roll out flat. Even after the strike you can see the rolling lines. They can get lighter after the strike. But when you get a OBW (Original-Bank-Wrapped) roll, then you can see that these lines can be in different directions. That tells me that these are not on the die, but on the planchets. The multiple directions from the original roll with the lines in different directions from the planchets rotated differently from strike to strike.

While these are light on this image, you can see the rolling lines in different directions. (also note the dies used on these coin shows they were from the same dies.

On an off center coin you can see these rolling lines where the strike didn't happen and even after the strike you can see see these rolling lines:

So on your coin the Struck Through Grease allows the rolling lines to still appear even after the strike happened, even stronger on areas where the strike was prevented by the grease.