Just a quick info about the Editor and VSync: It seems, that to get VSync actually working properly with the Editor, you need to use a special console command.
I had some graphic problems in some of my 2D test projects, which were VSync related, and it turned out, that VSync never actually worked on my machine in the editor, despite it being turned on.
Use that command to make sure, that it works for your editor too, then maybe you can figure out more easily, what is going on with your code and counter. (i just added that to my character at the “Begin play” event)
Got the tip from there: