This is reproducible only in the FluentTheme. Setting the RadCollapsiblePanel.SmallButtonsPerColumn to 3 does not make any difference. The workaround is to set a higher value for the ContentHeight property of RadRibbonView, for example 120px. The fix for this issue will be available with LIB (version 2018.3.1203) published on Monday, 3-rd December, 2018.