Unable to Update App on Play Store After Migrating from Kotlin to Flutter (Same Package Name)

I have an Android app that was originally developed using Kotlin and published on the Google Play Store two years ago. I recently migrated the app to Flutter while keeping the same package name and tried to upload the new version as an update to the Play Store. However, when I try to update the app on a device that already has the Kotlin version installed, I encounter the following error message in the Play Console:

"Try again, and if it still doesn't work, see common ways to fix the problem."

Steps to Reproduce:

1. Install the old Kotlin-based app from the Play Store.
2. Upload the Flutter-based version of the app to the Play Store with the same package name.
3. Attempt to update the app via the Play Store.
4. The update fails with the error mentioned above.

Things I Have Tried:

• Ensured the package name remains the same.
• Verified the version code has been incremented correctly.
• Signed the new Flutter app with the same keystore as the old Kotlin app.
• Confirmed the applicationId in build.gradle matches the original Kotlin app.
• Checked the Play Console logs but couldn't identify the specific issue causing the failure.

Question:

Why is the update failing when migrating from Kotlin to Flutter using the same package name, and how can I fix this issue to ensure a successful update on the Play Store?