Why custom User and Record Type Lookups are not filled in during insert operation?
I'm importing data from CSV source.
I have custom object with custom Lookup field to User object, but for any reason it is not filled in when inserting new records.
Your issue can be due missing RecordType.csv and/or UserAndGroup.csv source files.
To properly import lookup values, you need to provide ALL CSV source files, since the Plugin considers CSV files like a "virtual" salesforce org which has all those records present.