Xcode: "Scene is unreachable due to lack of entry points" but can't find it

In your storyboard, select each of the view controller (red arrow in image below) and look at the Storyboard ID field (red oval). None of the Storyboard ID fields should be blank. When you find one that is, that is the culprit.

While this thread is old, I didn't see an answer describing what worked for me, so here goes...

I had this error and visual examination of the storyboard showed that all of the view controllers appeared to be connected to the root view controller.

I tried naming all 17 of the view controllers in the storyboard (as in @bobnoble's answer). I used a naming convention based on the long name of the view controller, e.g. "jvc" for "Jobs View Controller". When I tried to build, I got an error message pointing to one of the view controllers as having a duplicate name. Tracking things down, I found that I had an actual duplicate of a view controller stacked exactly on top of its twin. I suspect it was cut-and-paste damage from a user interface experiment that I didn't back out completely.

Anyway, deleting the unconnected twin solved my problem. After that, I removed all of the VC names as they're not referenced in the code.

I just had this exact error with a simple single-scene Storyboard, and all I had to do to fix it was check the "Is Initial View Controller" checkbox for the 1 view controller in the Storyboard. I suspect Xcode used to check this box for you by default in this situation, but no longer does.

Check the box for exactly one of the view controllers in your storyboard and you should be good.