If you have regular logging turned on and you change to XML logging and at the same time change the log file pattern name, the app starts writing to the new log file.
You end up with </session> closing tag when there is no <session> open tag in the last log file created.
Only a small thing and in plain text log it is not important because it is unformatted.
I did not specifically test, but I think the issue is when changing the log file name template (or directory) that the open tags are not closed before writing stops on old log file. And also tags are not opened for the new log file.