Hi Barbara Matos,
I can observe from the images that the ‘tab group’ widget is not enabling vertical scrolling even though there are buttons beyond the window limit. This behaviour is explained in the documentation for ‘scrollable’ property in ‘point 2’ of additional requirements. Please refer the link below.
As a workaround for the scroller to appear, the child objects should be on the 1st quadrant assuming that the bottom-left vertex of the group boundary is the origin as shown in the image.
I hope this helps.