Best guess:
..and a recap: Open image (1) duplicate (2) make a new layer with transparency for a trace (3)
Gimp 2.8 or Gimp 2.10 each the same. The move tool will move the layer with the first 'solid' pixel under the cursor.
With (3) active and the cursor in a 'transparent' area 'solid' is layer (2)
Either, Make sure the cursor is on a solid pixel or Enable the 'Move the active layer toggle' (4) in the Move Tool options.
..and a recap: Open image (1) duplicate (2) make a new layer with transparency for a trace (3)
Gimp 2.8 or Gimp 2.10 each the same. The move tool will move the layer with the first 'solid' pixel under the cursor.
With (3) active and the cursor in a 'transparent' area 'solid' is layer (2)
Either, Make sure the cursor is on a solid pixel or Enable the 'Move the active layer toggle' (4) in the Move Tool options.