Rapid scrolling of a PathView can lead to invisible delegate items, either momentarily or permanently. The pathItemCount property appears to be the root cause of the problem.

Example video showing the problem in action.

The documentation has this to say regarding pathItemCount:

If a pathItemCount has been set, it is possible that some items may be instantiated, but not considered to be currently on the path. Usually, these items would be set invisible...

However, testing each delegate item in turn (including items that have turned invisible) indicates that each item's visible property is in fact true.