@JealousFish Yes,
In Qt Creator is called “Build Directory”, where file .o are created and where you find your application.
In the past I had the same issue, when I deleted the build folder the problem disappeared.
Sometimes, when compiler failed and the code seems ok, I delete the builder folder and the problem disappears.
I think, but it is only my idea, when this happens some files .o are locked, perhaps because I stopped the previous compile.