If you upgraded to 2.16.3 or 2.16.4 you will need to re-create your Scheduled reports as they will be empty (no recipients, no report selection, etc.). You have to re-create them manually, or you can also restore the table
piwik_report (containing your Scheduled reports definition) from a backup if you have one.
Piwik 2.16.5 has been released and fixes this issue.
We are sorry for any inconvenience caused.