When using annotation in D8 (e.g. when creating an entity), there are a couple classes annotation depends on. If you do not use them, you will get an exception that looks a little like this:
Additional uncaught exception thrown while handling exception.
I am pointing this out because confusion could be had if your IDE points out which classes you import but are not used. PHPStorm does not understand the annotation classes are required, so it will gray them out. It is tempting to remove things that are grayed out. (for me!)
Adding these may resolve the issue if it's annotation related.
I wanted to post in hopes that the search gods will pick this up for anyone stuck in that rut.