There are many reasons why this would happen. The only thing you could do is try the below steps and solutions one by one. This is mostly vscode error
Anyone of the solution may work with you.
Solution number 1
- flutter clean
- flutter pub get
Solution number 2
Remove about app.apk in /build/app/outputs/apk/app.apk and rebuild. VS code may have this problem. You may also try to run your in Android studio.
Solution number 3
1. flutter clean
2. flutter build apk