After latest maintenance, Confluence People directory is empty

After the last maintenance a couple of customers have found that their people directory is empty. This causes @mention and the Share Pages button to stop working.

This can be resolved by rebuilding the index. Simply to go to <yourdomain>.atlassian.net/wiki/admin/search-indexes.action and click on rebuild index. This will take a few minutes, after which the people directory will be correctly populated.