Comment 75 for bug 1480877

You might be running into those dbus blocking calls in the network-manager bearer backend.
The networkmanager bearer plugin currently is using a few blocking dbus calls to get properties and such.
see this abandoned change here:
https://codereview.qt-project.org/#/c/98090/

This change was abandoned as QNAM is synchronous in nature, and expects defaultConfiguration to be ready right away.

I have written a simple bearer backend plugin based on the connectivity-api that might be used instead.
This has one static configuration that it used.

https://codereview.qt-project.org/#/c/140752/