Some of the time when using my Document-based mac app (Xcode 10, Swift 4.2, macOS 10.13.5), I get the following error in the console:

_NSDocumentBasicAsyncOperation 0x60c000233c40 went isFinished=YES without being started by the queue it is in

I understand how this can happen when you're using asynchronous operations (see, e.g., this question), but I don't. This is something Cocoa does all by itself, so my question is how worried should I be, and how can I find out where this error comes from? I am overriding a number of functions in NSDocumentController and NSDocument; I suspect that it's something in NSDocument (I get one of these per open document), but I'm stumped where to start troubleshooting, and curious as to what may be going on.