In Qlik Sense February 20 release, the Qlik Centralized Logging Service handles communication outages with PostgreSQL by retrying three times to establish the connection and displays an error if unsuccessful. Communication outages with PostgreSQL can occur for a number of reasons and are not always recoverable in the limited retries of three times.
For example if the repository database is taking longer time than the total time of 3 retries before it is up and running.
A suggestion is to restart the centralized logging service after 3 retries, then loop the same 3 retries / restart until communication is established with repository Postgres repository database.