Notifications

I'll check... I haven't done any changes since the last updates I don't think... I'll check on those menu items.

517 is an unused community wall (CB Activity). It was set to Members group, I set it to public, but no change.
Weirdly, all the same links before the last update work fine, but the new ones don't.

Unpublish that menu item entirely and see if your issue persists.

I did that, then I trashed it, and then deleted it completely, cleared cache, same issue. 
Then switched off SEO friendly again, this time the url is: ../index.php?option=com_comprofiler&view=pluginclass&plugin=cbactivity&action=activity&id=2389&Itemid=4170
4170 is my publically available CB Activity wall.
Kind of weird.

I figured it out - but made another puzzle at the same time.
I looked at the activity streams, the "recent Activity" stream has disappeared. I'm sure I didn't delete it.
All that's left is the GroupJive stream, so I made the Activity menu link to the GroupJive stream and the links work... but now the main link to the activity stream shows "No posts to display."

Scratch that... the Recent Activity stream was just filtered out, it is there.
All these posts that are being separated from the Recent Activity stream are GroupJive posts, Maybe that helps?
It seems to be doing the same thing in my other communities.