I use SiftingAppender with RollingFileAppender.
I found that when a RollingFileAppender managed by the SiftingAppender timeout, the SiftingAppender stop it and throw it away.
But, when the same RollingFileAppender is triggered with the same MDC, the SiftingAppender attempt to build a new one and start it.
Because the previous RollingFileAppender register itself with fileNamePattern in the Logger Context's FA_FILENAME_COLLISION_MAP and never remove it, the new one cannot start, and no log will be output.
So, I suggest that when the RollingFileAppender stopped, remove the key it previous registered in the Logger Context's FA_FILENAME_COLLISION_MAP.
And, I think it will also happen to FileAppender.