If I save a pdf to iCloud Drive and try to mark up using apple pencil, at some point in the process it locks up, no longer responding to the interface buttons (but still allowing you to draw with the pencil). Any edits I make beyond this point, however, will not be saveable or exportable and are lost when I restart the iCloud Drive app. If I only do a few strokes, it will save/export fine, but somewhere along the line I hit a point where my work is lost. This is REALLY frustrating and disappointing. This feels like one of the core built-in benefits to the apple pencil and at least on my machine its utterly broken.