Hello @apa64
thanks for your feedback, and for sharing a work around! 
As you’ve seen with the LTS helm chart definition, the pod Liveness is directly mapped to the api/system/health SonarQube API endpoint, which provides a slightly different information:
That’s the case only for the LTS chart though. With SONAR-15239 a liveness endpoint was added to SonarQube 9.1+ API. The 9.x helmchart relies on this new endpoint and should not suffer from any such upgrade problem.
Warning: the last step of the work around described by Antii is to come back to the original chart, this is important as the work around practically disables the livenessProbe
Alternative: Another work around would be to apply the upgrade before the move to K8S.