Things to check
User Report must be a system level user report (a user cannot choose company level user reports for Advanced Automation)
Does the User Report have an Export Type of Flat File
If a filter prompt is used on the User Report, only ONE prompt is used
If a filter is used, it is active
Report prompt filter ID is based on the selected Data Type and/or Data Source to be used in the Quick Workflow
For more details see: How to create a user report for importing for Advanced Automation
Watchouts
Once a user report is selected it will always appear in the drop down list regardless if the report is changed and no longer meets the user report requirements up until a different report is selected.
If there is no filter in the user report, the user report will appear in the drop down list but note the import will use only the first row of data from the user report if the the checkbox is ticked. If unchecked, all records from the user report will be processed up to the system preference field which is set at 1000 and can be changed.