Entries in timesheets have been reported as being deleted automatically, without the end users doing it. A data extract of all timesheets and time entries for the affected period, taken before the incident was reported, show that there were entries against these timesheets. And that these timesheets were posted.
Exact cause is unknown.
Likely causes are as below:
It is recommended to use System Actions to approve timesheets. It is unsupported to execute UPDATE statements against out of the box tables.