I have discovered that if you take a texture, size it via 'Real World Scale', feed it through another component (I know of two), and then feed that into a UVW Randomizer, it will cause the 'Randomize Each Tile' function within the UVW Randomizer to not work correctly. It doesn't appear that Corona Tri-planar affects this issue at all.
I've attached a Max file that feeds a checker map through a 1) map input of a Gradient Ramp and 2) a Corona Mix, and when 'Randomize Each Tile' is enabled, it causes a speckled appearance.
This has been problematic for me because I use both Corona Mix (to multiply blend maps together) and Gradient Ramp on a lot of materials in my projects. I think a work around for now would be to use the RGB Multiply map to blend my textures together.