I have the following UserDataPersister (taken straight from the tutorial) configured:
Information for Service "App\DataPersister\UserDataPersister"
============================================================= 
  Service ID       App\DataPersister\UserDataPersister            
  Class            App\DataPersister\UserDataPersister            
  Tags             api_platform.data_persister (priority: -1000)  
  Public           no                                             
  Shared           yes                                            
  Abstract         no                                             
  Autowired        yes                                            
  Autoconfigured   yes                                            
and the following User fixture:
App\Entity\User:
    user_{1..10}:
        email: "usermail_<current()>\\@email.org"
        plainPassword: "plainPassword_<current()>"
        __calls:
          - initUuid: []
But I get errors when loading this fixture:
  An exception occurred while executing 'INSERT INTO "user" (id, uuid, roles, password, email) VALUES (?, ?, ?, ?, ?)' with params [281, "16ac40d3-53af-45dc-853f-e26f188d  
  1818", "[]", null, "usermail1@email.org"]:                                                                                                                                
                                                                                                                                                                            
  SQLSTATE[23502]: Not null violation: 7 ERROR:  null value in column "password" of relation "user" violates not-null constraint                                            
  DETAIL:  Failing row contains (281, 16ac40d3-53af-45dc-853f-e26f188d1818, [], null, usermail1@email.org).                                                                 
My implementation of UserDataPersister is identical with this.