First off, color harmony is just cool!
When associating a color harmony to more than one node in the mesh fill will cause X6 to crash when adjusting grid size.
Create a color harmony and rectangle.
Add a mesh fill to the rectangle and select all of the nodes.
Double click on one of the color harmony swatches to associate.
Adjust the grid size.
Crash will not occur if only one node is associated to a color harmony.
Crash must have color harmony nodes associated in the same direction as the grid nodes being adjusted. In other words, if the nodes associated with the color harmonie are in a horizontal direction, then adding grid nodes horizontally will crash it.