This issue is known to happen with Wacom styluses.
After opening of some dialog boxes, the Brush Library and Brush Palette no longer seem to register the tap-hold to activate moving brushes.
The tap hold and move will scroll the window, but the brush does not ‘pop out’ to be moved around.
This will happen after use of some brush commands from marking menu (all have a dialog box):
Import Brush Set
When this happens, the quickest means to restore the proper behaviour is to tap on the marking menu icon and make a slight gesture. Upon doing this action, tap-hold using the Wacom stylus will be re-enabled.
Alternatively, behaviour is restored with:
a mouse click and hold
minimizing and maximizing Sketchbook Pro