FluencyLogbackAppender : logs missing when exec time is small

[BurnSaibot]

Hi,
we are using your FluencyLogbackAppender to collect logs on a distributed system. It worked perfectly until we tried to add a logger to collect data about tools used to manage the system, for debugging purpose. Logger use a File appender and a FluencyLogbackAppender.
Thing is, some of these tool have a very small time of execution ( like 5s for example) and we detected that the FluencyLogbackAppender seems to not have enough time to send the logs. Adding a Thread.sleep(5000) in main thread seems to "fix" the problem, but we can't afford to do so.
I checked fluency documentation and call to close() should wait until all messages are sent (https://github.com/komamitsu/fluency#wait-until-buffered-data-is-flushed-and-release-resource).
I saw fluency.close() is called in the stop() method of FluencyLogbackAppender

logback-more-appenders/src/main/java/ch/qos/logback/more/appenders/FluencyLogbackAppender.java

Line 78 in 2b2b38d

public void stop() {

and can't understand why logs are not sent. Is it a configuration problem ?