Load signals not emitted when opening a google result

After making a search on Google and clicking on a link, the load of the "clicked" link does not trigger any load signals.

acceptNavigationRequest() is called.
urlChanged() and faviconChanged() are emitted.

But none of loadStarted(), loadProgress() and loadFinished() are called.

Qt WebEngine 5.15.4 does not have this issue.

More info

The issue does not happen when using a Chrome/Chromium user agent.
The issue happens when using (at least) Firefox or Safari user agents.

Adding the following code in the main of the simplebrowser allows to reproduce the issue:

 QWebEngineProfile::defaultProfile()->setHttpUserAgent("Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:89.0) Gecko/20100101 Firefox/89.0");

Also when it happens the acceptNavigation() gives NavigationTypeRedirect while it gives NavigationTypeLinkClicked when using a Chromium user agent.

With Qt WebEngine 5.15.4, when using a Firefox user agent, acceptNavigation() still gives NavigationTypeRedirect, but signals are emitted.