QML application hangs and cycle power is required

[Mark81]

I'm facing a weird problem. I'm working on a Qt5.7 / QML project from several weeks. Sometimes my application hangs on startup, and in three different situations:

• QQmlApplicationEngine::load() never returns
• QQmlApplicationEngine::load() returns, the QML file is processed but nothing is shown
• QQmlApplicationEngine::load() returns, the QML file is processed, it displayed for a while and then it hangs

If the application starts successfully it works fine for many hours with no problem at all. It doesn't (stricly?) depend on my code because it happens also with "helloword" applications, say a QML page with a Rectangle and a C++ Class that does nothing.

When this happens, I need to power cycle the RPi. Killing the process or event reboot the system it's not enough! The application will then hang always as in the first point, no matter how many times I start it.

The o.s. seems to work anyway, i.e. I can use the system but I cannot launch any QML application! Some further details about the system:

• RPi3 powered with a 5V 3A wall power supply
• Raspian Jessie Lite (kernel 4.4.11-v7+)
• Qt5.7 compiled from sources
• EGLFS backend, no X server

I also checked the CPU temperature (/sys/class/thermal/thermal_zone0/temp) and it never rises over 65 °C. But I guess a thermal issue should hang the whole RPi not just a process!

What should I do to investigate further?