On mediawiki.org in latest Chrome on Mac. Notifications from other wikis enables.
The alerts icon in the personal toolbar showed a 3. (Though grey, not red. When the notification is from the local wiki it shows red. Not sure this is on purpose but it seemed somewhat arbitrary to me.)
When opening the alerts drawer, it again mentions there are three, and it mentions the three wikis. In actual rendering below that only 2 notifications are shown. There is an empty section for the first wiki mentioned.
After clicking on the empty section nothing happens. Reloading the page results in the number having gone down to two. Now the same problems happens with the first one of this. The notification previously shown is now hidden.