The Activity column on the main page of Phabricator is rendered three times, one under another.
Thanks! Weird; I have no idea what happened. I don't see any changes in the last six weeks to the Dashboard content either.
However we pulled a new software version in Phabricator (2019-07-03).
Fixed by removing the duplicates from https://phabricator.wikimedia.org/dashboard/view/1/
(Notes to my future self: As usual I've been baffled by the UI. Somewhere in the middle of the scroll, after all widgets have been displayed, but before the "Dashboard Used By" section and the history of changes to that Dashboard, I finally found some lost "Create Panel" and "Add Existing Panel" buttons which are at the end of each respective column. And the "Manage Panel" dropdown of each panel allows to remove a panel from a column.)