Java log4j2: Log messages go missing sporadically, especially in multi-threaded scenarios

[hexagon-ecosys]

Expected behavior

All log messages should be sent to App Insights

Actual behavior

Log messages go missing sporadically in multi-threaded scenarios when several threads are logging simultaneously
Application Insights log file has no errors

To Reproduce

Clone https://github.com/hexagon-ecosys/azure-app-insights.git and run it several times by supplying the single parameter value '3' (which runs it in multi-threaded mode with long messages upto 20K characters in length)

System information

• App Insights 3.4.18
• MacOS 14.2 and Alpine 3.18 with Eclipse Temurin JDK 21

Additional Information

• I cannot not see any pattern to this issue other than the fact that it happens more during weekdays (we're based in New York City) and less during the weekends
• I am using the preview option generalExportQueueCapacity. Without it, I can see error messages in the Application Insights log file asking that it be set

[michaldaniel]

I'm experiencing something very similar where there are portions of log messages missing from the same logger output executed at different time and we are also using log4j2 and there also seems to be no obvious pattern (using version 3.4.19 integrated with JVM argument).