When I have pods issues, I often do a full clean to have a fresh install :

flutter clean
flutter pub cache clean 
rm -rf Pods
rm -rf .symlinks
rm -rf Flutter/Flutter.podspec
rm Podfile.lock
rm -rf build
rm -rf ~/Library/Developer/Xcode/DerivedData
flutter pub get
cd ios
pod repo update
pod install
cd ..
flutter build ipa --release

Maybe that can help you.
Warning : 'flutter pub cache clean' => it cleans all the pubs you have in cache, for all projects. You'll have to run 'flutter pub get' in every single project you want to open.