QtQuick Application window not showing up, process gets stuck

Trying out Qt 5.9.2 with my current active project results in no window showing up. Everything compiles without errors, there are no runtime errors, warnings or any output whatsoever.

The app process starts, but only uses up 10 mb of ram, which is rather low for even an empty qtquick project, and no cpu activity - it is not freezing, it is simply not showing any output.

I also tested with a custom build, as well as with the 5.10 beta, the same issue.

Note that the project works perfectly well with previous versions of Qt, all the way from 5.9.1 to 5.7. So whatever is causing this, it was introduced recently, as it only affects 5.9.2 and 5.10.

Unfortunately I have problems isolating and reproducing the issue, the project it manifests in is big, complex and I am not at liberty to share the code.

All I can tell for sure is that there is a problem that wasn't previously there. Also, the actual symptoms are very similar to this other bug I reported, which is presumably caused by some bad circular reference checks - literally the same thing happens, no window, no output, no errors, no nothing:

https://bugreports.qt.io/browse/QTBUG-56292