I have a Flutter project that initially did not have a .gitignore file. After adding the .gitignore file and cleaning up with the following commands:

git rm -r --cached .
git add .
git commit -m "fixed untracked files"

It worked perfectly at first, until my Flutter project built the application for Android. Then, several files in the gradle folder, which had previously been included in the .gitignore, reappeared.

6 files appeared

I ran the commands above again, and the files disappeared, but when building the apk again, they reappeared.

.gitignore:

# Do not remove or rename entries in this file, only add new ones
# See https://github.com/flutter/flutter/issues/128635 for more context.

# Miscellaneous
*.class
*.lock
*.log
*.pyc
*.swp
.DS_Store
.atom/
.buildlog/
.history
.svn/

# IntelliJ related
*.iml
*.ipr
*.iws
.idea/

# Visual Studio Code related
.classpath
.project
.settings/
.vscode/*

# Flutter repo-specific
/bin/cache/
/bin/internal/bootstrap.bat
/bin/internal/bootstrap.sh
/bin/mingit/
/dev/benchmarks/mega_gallery/
/dev/bots/.recipe_deps
/dev/bots/android_tools/
/dev/devicelab/ABresults*.json
/dev/docs/doc/
/dev/docs/api_docs.zip
/dev/docs/flutter.docs.zip
/dev/docs/lib/
/dev/docs/pubspec.yaml
/dev/integration_tests/**/xcuserdata
/dev/integration_tests/**/Pods
/packages/flutter/coverage/
version
analysis_benchmark.json

# packages file containing multi-root paths
.packages.generated

# Flutter/Dart/Pub related
**/doc/api/
.dart_tool/
.flutter-plugins
pubspec.lock
.flutter-plugins-dependencies
**/generated_plugin_registrant.dart
.packages
.pub-preload-cache/
.pub-cache/
.pub/
build/
flutter_*.png
linked_*.ds
unlinked.ds
unlinked_spec.ds

# Android related
**/android/**/gradle-wrapper.jar
.gradle/
**/android/.gradle
**/android/captures/
**/android/gradlew
**/android/gradlew.bat
**/android/local.properties
**/android/**/GeneratedPluginRegistrant.java
**/android/key.properties
*.jks

# iOS/XCode related
**/ios/**/*.mode1v3
**/ios/**/*.mode2v3
**/ios/**/*.moved-aside
**/ios/**/*.pbxuser
**/ios/**/*.perspectivev3
**/ios/**/*sync/
**/ios/**/.sconsign.dblite
**/ios/**/.tags*
**/ios/**/.vagrant/
**/ios/**/DerivedData/
**/ios/**/Icon?
**/ios/**/Pods/
**/ios/**/.symlinks/
**/ios/**/profile
**/ios/**/xcuserdata
**/ios/.generated/
**/ios/Flutter/.last_build_id
**/ios/Flutter/App.framework
**/ios/Flutter/Flutter.framework
**/ios/Flutter/Flutter.podspec
**/ios/Flutter/Generated.xcconfig
**/ios/Flutter/ephemeral
**/ios/Flutter/app.flx
**/ios/Flutter/app.zip
**/ios/Flutter/flutter_assets/
**/ios/Flutter/flutter_export_environment.sh
**/ios/ServiceDefinitions.json
**/ios/Runner/GeneratedPluginRegistrant.*

# macOS
**/Flutter/ephemeral/
**/Pods/
**/macos/Flutter/GeneratedPluginRegistrant.swift
**/macos/Flutter/ephemeral
**/xcuserdata/

# Windows
**/windows/flutter/generated_plugin_registrant.cc
**/windows/flutter/generated_plugin_registrant.h
**/windows/flutter/generated_plugins.cmake

# Linux
**/linux/flutter/generated_plugin_registrant.cc
**/linux/flutter/generated_plugin_registrant.h
**/linux/flutter/generated_plugins.cmake

# Coverage
coverage/

# Symbols
app.*.symbols

# Exceptions to above rules.
!**/ios/**/default.mode1v3
!**/ios/**/default.mode2v3
!**/ios/**/default.pbxuser
!**/ios/**/default.perspectivev3
!/packages/flutter_tools/test/data/dart_dependencies_test/**/.packages
!/dev/ci/**/Gemfile.lock
!.vscode/settings.json
.fvmrc
.fvm
android/.gradle/**/executionHistory/executionHistory.bin
android/.gradle/**/executionHistory/executionHistory.lock
android/.gradle/**/fileHashes/fileHashes.bin
android/.gradle/**/fileHashes/fileHashes.lock
android/.gradle/buildOutputCleanup/buildOutputCleanup.lock
android/.gradle/buildOutputCleanup/outputFiles.bin

The same commands have also been run, and git removed those 6 files. However, when building the Android files, those files reappeared.