QtQuickControls2 Examples of Qt WebAssembly won't work well

[LeonZJU]

I built both the threaded(configure with -feature-thread) and non-threaded(configure without -feature-thread) versions of Qt Wasm using the following environments:
Qt: 5.14.2
emsdk: ./emsdk install sdk-fastcomp-1.38.30-64bit
OS: CentOS8.1
GCC: 8.3

Most of the examples build and run well.
However, with threaded build, all the QtQuickControls2 examples lead to a massive CPU usage and a continuous huge memory increase while the browser compiling the apps.
And with the non-threaded build, the "gallery" app works fine but all other apps in the QtQuickControls2 examples just freeze while compiling(keep display "compiling").

Does anyone know why? Thanks for your help.