I couldn't find any existed post with this problem, so posting it here, maybe someone saw something similar.
After upgrade to version 5, sometimes notifications are not displayed after action. I am talking about standard notification "Saved", e.g: after saving edit form. Most of the times it's fine, but it's often not. I was able to replicate it on my local by opening couple of record in new tab, saving them. If not reproduce - opened another batch of forms. With 2nd batch I was able to reproduce that.
never comes. Once page enters this "failed" state, it doesn't matter how many times "Save" button is pressed - notifications won't be shown. If page reloaded (or opened another page) all those "pending" notifications will be displayed.