I used a few snippets for testing and now they are alle locked. Select all and delete does not work. Moving selected snippets out of storyboard causes the well known bursting cloud but the are still there. Sometimes they are duplicated instead of deleted. See 2 screenshots:
Dragging all of the layers away only deletes the unlocked layers. The locked layers remain. You need to unlock them FIRST before they can be deleted. Easiest way is to click on a single layer to select it, then right click, and you’ll see a drop-down menu with the word “Locked” and a checkmark to the left of it. Click “Locked” and the checkmark goes away. That layer is now unlocked, and you can delete it. If you want to delete more than one locked layer at a time, Command-click on each of the locked layers to select only them, then right click to see the drop down menu. Again, click on the checked Locked menu item, it will unlock all of the selected layers, then you can delete them.
your hint worked perfectly. But why are layers locked? I did’t that
I guess when they created a few of the included snippets that they decided to lock some layers, making it less likely for the user to accidentally move them. In the one you included, I think it’s like a smokey or cloudy image that’s not intended to be moved. If it’s locked, then you wouldn’t be able to accidentally select it when you went to the stage to work on the slide (like clicking on the name title). You can lock and unlock YOUR OWN layers just as easily.
100 point to @stantastic. Perfect explanation. Thanks!