Linker failure to unused method

While writing a method for the derived QObject class, I accidentally named it setCustomEvent(). After building the project there were linker issues and I realized my mistake.

After refactoring and changing the method name to logCustomEvent() I tried to rebuild once more. Now neither the mainwindow class nor the derived class use that method name, but linker throws issue for both of them (mainwindow never even had a method with that name):

mainwindow.obj:-1: error: LNK2001: unresolved external symbol "protected: virtual void __cdecl QObject::setCustomEvent(class QEvent *)" (?setCustomEvent@QObject@@MEAAXPEAVQEvent@@@Z)

gazecomunicator.obj:-1: error: }}{{LNK2001: unresolved external symbol "protected: virtual void __cdecl QObject::setCustomEvent(class QEvent *)" (?setCustomEvent@QObject@@MEAAXPEAVQEvent@@@Z)

I tried following:

• Clean project + Run Qmake + Rebuild project
• Manually deleting build folder and repeat clean+qmake+build
• Removing Q_OBJECT macro and comment out all signal/slot uses, then add it back
• Adding the setCustomEvent() method to both mainwindow and derived class. (Linking still fails for mainwindow but the issue disappears for derived class)
• Rolling back the code to the point where I know it worked and make clean+qmake+build
• Deleting the code and making a fresh clone from git

Nothing seems to work and the linking issue always appears

UPDATE: The same issue exists after porting to MSVC2017 and trying to build

UPDATE 2: Bug disappeared after reinstallation of Qt (identical  options; Qt Creator 4.6.0, Qt 5.10.1, MSVC 2015 MSVC c++ 15.0)