I don’t know if this is only appearing on ecosystem beta instances, but my development site has a new content menu layout:
Unfortunately, it is breaking add-on menu links. In the screenshot above, both the “Slack Notifications” and “Feature” links are broken. When you click on them, depending on the user context, you fall through to an empty JIRA page with an error flag or JSD portal.
I can’t find anything about this change being documented anywhere so far. But since it has also broken the “Slack Notifications” menu link, I suspect it’s not intentional. Hopefully, this isn’t being rolled out across production sites.