Webform submission import: failed to import a lot of records executed in multiple batches

Nice! I came across the same issue. I used a similar patch and it solved my problem. The only difference is when checking for an empty line, I copied the logic from L422. I'm not sure if there are situations where this will actually make a difference, but I'll upload it anyway.

Corrected the patch format (missing the first line) in the previous 2 patches.

Does the CVS that is being imported have empty lines?

Can you upload and example CSV that is having this issue?

Patch #3 solved an issue I was having with big CSV's.

Patch #3 also worked for me. I was importing a CSV with 1900 lines. Without the patch, the completion message said it created a little under 300 records and then updated 1600 or something, even though I added sid and uuid columns so they should have all been recognized as unique. With the patch, the the upload completed successfully and I've got 1900 submissions now.

I think ths issue is not specific to big CSVs but to big CSVs that contain entries with line breaks, as they get interpreted as new lines with fgets where they should not.

I was facing the following errors in my case because of multiline webform elements:

...
>  [warning] Line n°101: 28 values expected and only 3 found.
>  [warning] Line n°102: 28 values expected and only 5 found.
...

Using fgetcsv as suggested seems to be the way to go, and I can confirm that the patch in #3 does solve the issue as it counts lines in a similar way to \Drupal\webform_submission_export_import\WebformSubmissionExportImportImporter::getTotal, although the latter uses if (!empty($line) && !is_null(array_pop($line))) { instead of if (!empty($line) && $line !== ['']) {, I'm not sure which approach is the best.

Thanks! :)

Patch #3 and the merge request do not seem to correctly recognize empty lines.
According to https://www.php.net/manual/en/function.fgetcsv.php, fgetcsv() returns an array containing only NULL ([NULL]) for empty lines.
In this code, it's strictly comparing with [''], so it will always return false.

$fp = fopen('php://memory', 'rw+');
fwrite($fp, <<<CSV
a,b,c

1,2,3
CSV);
rewind($fp);

while (($line = fgetcsv($fp))) {
  if (!empty($line) && $line !== ['']) {
    // This is always output.
    echo "not empty\n";
  } else {
    echo "empty\n";
  }
}

The first patch I submitted does not have this issue. The empty line detection method in that code is aligned with the existing condition in modules/webform_submission_export_import/src/WebformSubmissionExportImportImporter.php.