Hi,
this is ES related, set loglevel to DEBUG and check es.log, sonar.log, web.log
also
Not sure if Sonarqube 6.7.7 supports Java 13.0.1 already !?
You won’t get support for 6.7.7 anymore, use the latest version 8.0
or LTS version 7.9.1 instead => Download | SonarQube
for LTS you need to scroll down and choose your edition
Gilbert