All the animations made with the Xcode editor in .sks files start paused in my projects, but I see that in examples of books and tutorials the same thing does not happen and the animations are executed as soon as the application is started.
Putting the property of SKSpriteNode, isPaused = false solves it if the object is not anyone's child, if you do not have to go through all the nodes assigning the value to false (at least in the tests that I could do).
I have also seen that if in the didMove method you do the following, it works:
self.isPaused = true
self.isPaused = false
I do not know if it is an XCode bug or a behavior that you have recently modified (my version is 9.3.1) ?.
If it is a "normal" behavior, can it be modified by some preference or configuration (info.plist, .sks, or similar) so as not to be assigning that property by programming continuously?