1) Created new project.
2) Selected google map created.
3) Debug google_maps_api.xml steps followed.
https://console.developers.google.com/f
I think your still using your SHA1 for debug.keystore on your release build.. try to get your SHA1 on your release keystore.
Windows Terminal
keytool -list -v -keystore "{PATH OF YOUR RELEASE KEYSTORE}" -alias {ALIAS} -storepass {StorePassword} -keypass {KeyPassword}
OSX Terminal
keytool -list -v -keystore {PATH OF YOUR RELEASE KEYSTORE} -alias {ALIAS -{STORE PASS} android -keypass {KEYPASS}
Get your SHA1 and register it on your Google API Console..
Hope it helps. .