All Scheduled Reports in Performance Center were removed or deleted but without known user interaction.
Undetermined without ability to reproduce.
All supported Performance Management releases
To resolve this the Scheduled Reports were recreated. They remain and have not been removed again.
Without ability to reproduce this we can't debug it to determine a root cause.
There is also no debug available for Scheduled Report creation or removal in the product at this time.
If the problem is observed in a repeatable manner, please open a support case for investigation.