Steps to reproduce: Start a fairly big Qt project in the debugger (lldb). Break on a breakpoint. Expand a variable derived from QObject or QWidget (e.g. mainWindow). The debugger freezes instantaniously, only a flower like waiting cursor is displayed. The debugger has to be aborted now.

This unwanted behaviour disappears once "Use Debugging Helpers" under "Manage Kits"-> "Debugger">"Locals&Expressions" is disabled, so the bug must be somewhere in the python scripts that are executed when the debugger hits on something that is in the Qt namespace. 

The bug is not new, it has been there for more than 5 years. I always thought it is my computer configuration, but other people have the same issue (see https://stackoverflow.com/questions/64303152/local-variables-and-expressions-do-not-show-while-debugging-in-qtcreator-4-13-0/64308779#64308779) - that's why I reported it now finally