Tuplets within beams
Tuplets that contain notes that produce beams are also beamed together, but special beam grouping rules apply to tuplets within beams that also contain non-tuplet notes.
The default setting for a tuplet in a beamed group with secondary beams is to split the secondary beam and to show the tuplet with a bracket. The primary beam is not split.
You can alter the appearance of the bracket by selecting the bracket and changing relevant properties in the Tuplets group of the Properties panel.
The default setting for a tuplet in a beamed group with only a primary beam is to separate the tuplet entirely. However, you can change this setting on the Beam Grouping page in Notation Options.