QWebEngineView has no display in ubuntu-desktop-lxde-vnc docker container

[deeperblue]

I'm developing a simplest webapp using PyQt5. However, the QWebEngineView has no display in ubuntu-desktop-lxde-vnc docker container(index.docker.io/dorowu/ubuntu-desktop-lxde-vnc), while which in Chromium is OK.

The webpage had been loaded, for the contents can be shown while selecting and dragging them (Notice the console's output: "Falling back to using screens root_visual"),

but disappear right after the dragging was off.

Is there anyone has met the same problem?