Animate Pro 2 : Timeline Drop

I am a new Animate Pro 2 user. When I work hand-draw animation , It often show timeline drop. Everything lost and I can not undo my work. A timeline show only untitled name and empty layer. I see in lists of undo and show the word “timeline drop”. I can not understand.

Thank You
Animate Pro 2
WACOM intuos 4
Macbook Pro Retina 15"

You are in the Toon Boom Studio forum, you should ask your Animate Pro questions in the Animate Pro user forum instead.

You have not explained enough but from your screenshot I suspect that you are creating everything inside symbols which is rather cumbersome in Animate Pro. You probably need to enter the symbol to see the elements in the timeline that are inside the symbol. Remember that in Animate Pro, symbols should only be used as containers for elements whose position to each other never change (such as a tattoo on an arm). In almost every other case it is actually more awkward to use them (instead of simply making a group in the timeline) if you must have your elements grouped.