The two likely causes are undersized touch targets and overlapping input regions. Touch input is less spatially precise than mouse input because the contact area of a finger is larger and less exact than a pointer cursor. Microsoft’s touch-target guidance states that interactive UI elements must be large enough for users to access accurately, and recommends a target size around 7.5 mm square, approximately 40 × 40 pixels on a 135 PPI display. Earlier Microsoft touch-design guidance similarly emphasizes that controls must be appropriately sized for touch and identifies approximately 9 mm as a minimum targeting area. Therefore, small input buttons may fail to trigger because the user is not actually hitting the active target area. Overlap is also a valid cause: when two active regions occupy the same physical screen area, hit testing may route the touch to a different element, or the effective target area may be reduced. W3C accessibility guidance explicitly treats overlapping targets as reducing measurable target size unless the overlapping controls perform the same action. Event handlers themselves are not the defect; they are the normal mechanism for processing input. “Touch screen not initialized” is not a standard HTML5 application cause. References/topics: touch input, event handling, hit testing, target size, overlapping controls.