When I scale a layer it disappears..Why?

[Blighty]

(02-05-2020, 11:42 PM)marigolden Wrote: I scale this item in a layer bigger

I am not quite sure what you are doing here. If there is no selection the entire layer is scaled. If you do have a selection the selected area is scaled and becomes a new floating layer. Usual procedure would then be to choose "To new layer".

If you are enlarging the layer it could be that the layer is now larger than the canvas.
Use Image > Fit canvas to layers