AsyncQueueFullMessageUtil.transform modifies message format, dropping message format and parameters, and concatenates text to the formatted output.
It's a fairly common workflow to write a message implementation which outputs json or some other structured data (e.g. request logs) which are parsed by another mechanism. This often uses PatternLayout with pattern "%m%n". The current implementation of AsyncQueueFullMessageUtil concatenates a warning to the formatted message, which can break parsers.
Proposal: Avoid modifying the message itself in favor of using StatusLogger.warn when messages may be logged out of order.