Unwanted red lines when the unwind segue is performed

Question

I have a view controller, embedded in a navigation controller, which has a button and connects me with another view controller with a button. I have ctrl dragged from the button of the second view controller to the exit in the Storyboard creating an unwind segue. While the unwind segue works as wanted (When I click the button it removes the current view controller and gets me to the first view controller) but once that happens my current view has some red lines for no apparent reason. Why does this happen? Has to do with my Xcode installation or does it have to do with Xcode in general?

I have Xcode 10.1 and although there is nothing fancy in my code here it is anyway:

import UIKit

class PresentedViewController: UIViewController {
    @IBAction func myUnwindAction(unwindSegue: UIStoryboardSegue)
    {
        print("You learned to use unwindSegue")
    }
}