Debug error when slots are called

Attached the .h and .cpp files.

When the slots are getting called, debug error pop up (several times) - attached the screenshot of the error message.

Edit:

Adding the QT project to the issue for easy reproducibility of the issue.

Use case:

 Need to launch the login widget before the application starts and on success, I need to emit signal to launch another widget.

Using QT creator: 4.7.1

QT: 5.9.7

MSVC 2015, 32 bit

Using offline installer to install QT Creator and QT.