what version of log4net is Sitecore.Logging.dll branch/fork based upon?
There is a locking bug in log4net which affects version 1.2.10
https://issues.apache.org/jira/browse/LOG4NET-298
Which was fixed in version 1.2.14 & 1.3.0
https://issues.apache.org/jira/browse/LOG4NET-443
Looking to confirm the version that Sitecore uses, to make sure it's not affected.