The FailedSentOutStatisticsMessages.log is being generated in an environment where the Platform Analytics project has not been set up. The log file may take up several gigabytes of space and can quickly increase in size.
The log is populated with statistics from the Intelligence Server that failed to be sent to Telemetry Server. This typically occurs in environments where the Platform Analytics statistics have been enabled, but the Platform Analytics project is not set up.
To check if the PA statistics are enabled, execute the LIST ALL FEATURE FLAGS; command from Command Manager. In the output, the feature flag to be checked is Messaging Service for Platform Analytics.
Intelligence Server statistics captured by the log can be browsed and used outside of the Platform Analytics project. If this is not necessary, you can disable the Platfom Analytics Messaging Service to prevent the log from being populated with new data.