I've seen this on both E stable (20.6 with stable efl and elementary) and is more pronounced in Git with wayland where DND isn't fully implemented yet.
In the case you Drag something and for some reason the drop fails for whatever reason the icon you dragged disappears and reappears only after a refresh view. On stable after a failed DND in firefox it also borked the input and had to kill E on one occasion.
On wayland you can reproduce it as:
Drag a file (ie pdf) in terminology (it does nothing) and then try to drag it for a second time it dissapears.
On X its more tricky but i managed to do it a few times. Open terminology and drag a file on the top bar (approximately) if you try to drag the icon for a second time it disappears.