4-columns becomes 3-columns when screen widens

Greetings, I am experimenting with Clean Box and noticed that when using 4 columns of featured content, it will display 4 columns only at a specific width of screen. When smaller, the 3rd and 4th columns will move to the next row (normal) but if screen gets larger, it moves the 4th column to the next row and leaves a large background area where the 4th column should be. I get the same results with Chrome, MSIE11 and MS-Edge. No changes to theme core, just "customizer" options and no additional css. Possible glitch with "@media screen..." callout? Something for next update? Thank you!