It seems there is an issue with the material theme and nested grids. When you have master-detail nested grids, the entire last nested grid gets applied with the same styling as the bottom rows of all the other nested grid.
The styling in my browser is showing up as
Which causes the rows in the last grid to not appear.
I have attached an image where I have changed the styling to 5px and red so you can see that it is being incorrectly styled. You can see that even the other rows in in the last grid are getting styled along with the last row style.
I am running the latest version of Kendo.