If you are using the Google Play App Signing, the key that signs your release app is they Google Play-generated signing key, not the uploaded keystore.

This generates a different SHA-1 fingeprint which would most likely cause the blank map error.

You could create your Play App Signing SHA-1 through:

• Google Play Console -> Your App -> Setup -> App Integrity
• Copy the fingerprint under App signing key certificate

Add the SHA-1 to your API restrictions and your blank map should now render properly.