When the Weston display is rotated to use all the screen set vertically, some elements on the YouTube app as the "Skip add" button, or the video description/controls are not visible. All these elements work as expected when the vertical layout of the UI is displayed centered on the default horizontal screen resolution.

In order to rotate the view, it can be changed at /etc/xdg/weston/weston.ini:

[output]
name=HDMI-A-1
transform=270
#transform=0