Flat file enrolment don't work correctly.
The enrolment file IS in the good place, IS processed by the cron job, BUT it returns (in the cron print) errors "Unknown role in field2" for each enrolment
A solution i've found is to (as administrator) open the Flat File enrolment settings, and save them (without changing anything), just before running the cron. Doing so, it's well processed, without errors.
Seems like some short role names wasn't well taken...