In the Layaout - Available features section, there an error:

It's said:

[4 blocks] - it's a column layout selector, where you can change column structure inside the row based on twelve column system. Only one row is available in a single section. Choose one from predefined or set your own grid. Using Custom Layout remember that the summary of columns must be always 12. For example, you can insert 6+6 or 3+3+6 or 4+4+4+4.

It should be 4+4+4, instead of 4+4+4+4.