Files not being written in Gulp tasks

Question

I'm trying to create a Gulp task script to process language-specific data files (resources/{lang}/data.json), transform the data, and generate JSON files for each entry. When executing my Gulp tasks, no errors are reported, yet no files are being generated:

╰─❯ npx gulp                                                     
[14:21:29] Using gulpfile ~/repos/cemeteries/gulpfile.js
[14:21:29] Starting 'default'...
[14:21:29] Starting 'cleanCemeteryDir'...
[14:21:29] Finished 'cleanCemeteryDir' after 14 ms
[14:21:29] Starting 'generateContentFiles'...
[14:21:29] Starting 'bound generateContentFilesForLang'...
[14:21:29] Starting 'bound generateContentFilesForLang'...
[14:21:29] Finished 'bound generateContentFilesForLang' after 17 
[14:21:29] Finished 'bound generateContentFilesForLang' after 21 
[14:21:29] Finished 'generateContentFiles' after 22 ms
[14:21:29] Finished 'default' after 38 ms
File Friedhof-1.json created in content/de/friedhof
File Friedhof-2.json created in content/de/friedhof
File Cemetery-2.json created in content/en/cemetery
File Cemetery-2.json created in content/en/cemetery
...

╰─❯ ls content/en/cemetery                                        
ls: cannot access 'content/en/cemetery': No such file or directory

Has anyone an idea, what the problem might be?

The corresponding gulpfile:

import gulp from 'gulp';
import jsonTransform from 'gulp-json-transform';
import rename from 'gulp-rename';
import slugify from 'slugify';
import clean from 'gulp-clean';

const languages = ['de', 'en'];

function cleanCemeteryDir() {
  return gulp.src(['content/{en,de}/{friedhof,cemetery}'], { read: false, allowEmpty: true })
    .pipe(clean({ force: true }));
}

function generateContentFilesForLang(lang) {
  const slugs = new Set();

  return gulp.src(`resources/${lang}/data.json`)
    .pipe(jsonTransform((data, file) => {
      const baseDir = `content/${lang}`;
      const cemeteryDir = `${baseDir}/${lang === 'de' ? 'friedhof' : 'cemetery'}`;

      return data.cemeteries.map(cemetery => {

        const slug = slugify(cemetery.title);

        const cemeteryData = {
          ...cemetery,
          slug,
          head: {
            meta: [
              {
                hid: "description",
                name: "description",
                content: cemetery.description
              }
            ]
          }
        };

        const jsonFilename = `${slug}.json`;

        // Save each cemetery as a separate JSON file
        return gulp.src('dummy.json', { allowEmpty: true }) // Dummy source to trigger the task
          .pipe(jsonTransform(() => [cemeteryData]))
          .pipe(rename(jsonFilename))
          .pipe(gulp.dest(cemeteryDir))
          .on('end', () => console.log(`File ${jsonFilename} created in ${cemeteryDir}`))
          });
      });
    }));
}

function generateContentFiles(done) {
  const tasks = languages.map(lang => generateContentFilesForLang.bind(null, lang));

  gulp.parallel(...tasks)(done);
}

export default gulp.series(cleanCemeteryDir, generateContentFiles);