This only appears to occur on Windows 10. If the Windows regional advanced settings are changed to use a ',' character for both DP and grouping character the QLocale constructor will deadlock due to a recursive call while holding a lock.

This was reported for our application by users using the Greek language locale, without having to change the number formats to the pathological setup above. Can be demonstrated by a trivial application that just constructs a QLocale default object in main().