If I run phpcbf --sniffs="PSR12.Files.FileHeader,Generic.Files.LineEndings" myfile.php where myfile.php is as follows (with \r\n line endings):
Then I receive an error:
PHPCBF FAILED TO FIX 1 FILE
The file now contains 25 empty lines betwen the opening <?php tag and $name = 'Foo';. With \r or\n line endings the file is fixed as expected:
Tested with dev-master and v3.5.4.