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I recently upgraded my Ubuntu installation from 16.10 to 17.04. Since then, the notification bar has not displayed some of the icons that should be present when certain programs are running.
Both Skype and Slack are running, and previously displayed their respective icons in Ubuntu 16.04, which are missing after the upgrade to 17.04. (Due to the lack of the icons, this is a bit hard to illustrate. Note that both the Redshift as well as the Dropbox icon are still there, as well as the standard notification icons.)
Also, new notifications look strange (blue box) and have become non-clickable. The image shows an incoming Skype notification, which did not look like this before.
What has happened, and how can I revert to the previous (standard, I assume) behaviour?