Function passed in Qt.callLater() doesn't get called when the code is built in debug mode

When the attached code is built in the debug mode in Qt Creator, the function passed in Qt.callLater() doesn't get called. It works fine when the code is built in the release mode. I have tried Qt 5.13.1 GCC 64bit and Qt 5.14.1 GCC 64bit, and this issue can be reproducible with both releases.