No source code, You can reproduction this issue by the official Example.
I run this example on Qt-5.10.0 + Mac OSX 10.13.2, with two Display Device.
15.4 (2880 x 1800) devicePixelRatio=2
23.5 (1080 x 1920) devicePixelRatio=1
At the beginning, It runs fine on 15.4(2880x1800). After I drag the QML window to 23.5(1080x1920), It become empty.
I tested it on Qt-5.9.3, this issue didn't appear.