When I updated my wordpress installation to 5.0.1 I had the same problem. Using @rfmcomposer idea, I went through my plugins. The plugin that was causing the issue was deactivated!!! After deleting the plugin all the notifications came back and I could update the rest of my plugins. I am not sure if it was indeed the plugin’s fault or if the act of deleting a plugin kicked it into gear but that’s what happened to me. The plugin was WP comment field manager.
