Reports configured in version 15.8 are no longer visible on the System > Incident Deleter > Flag Incident For Deletion page in the 16.0 enforce console after upgrading.
Release : 16.0
Summarized reports will not be visible in version 16.0 and above.
The use of summarized reports in Flag Incidents for Deletion is not expected to work in 16.0.
We are aware that it did work in the previous 15.8 however that was a known issue, it was not supposed to work that way.
In 16.0 it has been deliberately removed as it would cause too many additional issues if kept in place.
So in v16.0 and above the reports you can use are those which are not summarized.
If necessary you may need to recreate the reports without summarization.