The correct causes are insufficient input target size and overlapping input areas. Touch interaction depends on hit testing: the browser or platform determines which element occupies the touched screen coordinate and dispatches the event to that element. If a button's active area is too small, the user's finger may visually appear to tap the button while the actual touch coordinate falls outside the actionable target. Microsoft's touch- target guidance recommends touch targets around 7.5 mm square, approximately 40 × 40 pixels on a 135 PPI display, to support reliable activation. Overlap is also a valid cause because one element can partially cover or compete with another during hit testing; W3C target-size guidance notes that overlapping areas should not be counted as usable target area unless the overlapping controls perform the same action. Event handlers are not the problem by themselves; they are the standard mechanism for detecting user input. "Touch screen not initialized" is not a normal HTML5 application-level cause. References/topics: touch input, event handling, hit testing, target size, overlapping controls.