A user is dragging and dropping within an app. If user presses left mouse button (LMB), quickly moves mouse with LMB down, then releases LMB without further movement, app receives one dragEnterEvent, one dragMoveEvent, but no dropEvent. However, if user quickly moves, pauses to wait for app to catch up, then moves mouse again, more dragMoveEvents are received (even if mouse then remains stationary) and a dropEvent is received.
App is accepting all events properly. All events are in a QGraphicsScene. Object being dragged is a pixmap, which might be slow. App uses PyQt5, which also slows it down. QDrag.setPixmap() is not called, so I am also receiving QPainter warnings see QTBUG 29283 but I think that is irrelevant.
I don't yet have a small test harness, but might be able to provide one, in PyQt.