OS: MacOS Mojave
Steps:
1- Register a log message handler (qInstallMessageHandler) that uses std::cout to print log messages:

         std::cout << msg << std::endl;
     

2- Run the application with debugger attached in QtCreator and observe the Application output pane

Outcome: Messages start printing but as time passes they become delayed

Expected: Messages are shown in output pane with minimal delay

Notes:

• Running without debugger attached shows no delays in Application output pane
• Printing the message in a file shows no delays for one observing the file with tail
• Delays are not observed with MacOS High Sierra