Using build-tools 35.0.0, apksigner 0.9, when verifying your APK:

INFO: SourceStamp: No digests available in the source stamp for signature scheme: 31

Are you getting a different result? Which build tools version? 

 Using --verbose is now showing the certificate information.

However, it gives false for Verified using v4 scheme (it's true for v3.1 scheme) 

 Don't worry, your signatures are in the event you published. Need to fix something in the app and it will be okay 

 Nice, thank you