This article provides brief information on reasons the log file rotation may not work.
All Kiwi Syslog versions
Using AutoSplit value can cause log file rotation to not work. AutoSplit value such as %DateISO is not usually combined with Log File Rotation. When you enable the AutoSplit value %DateISO, the CURRENT Log file age is always reset to 0 after creating new a filename.
If you really want log file rotation, DO NOT use AutoSplit value on the Path and file name of log file.