I deleted some test tickets using Admin > Setup > Reset Demo.
The counts of tickets in the agent interface left-hand pane still include the old tickets. How can I fix this?
Go to Tickets > Statuses > Archived.
Enable archiving if it is not enabled.
Click Reset search index to fix the counts.
You can disable archiving afterwards (you only need it if you have a very large number of resolved tickets - over a million).