I've noticed as on the same version a bug was opened which was closed with reason cannot reproduce:
Now we could reproduce constantly with our application but just on a single machine. I've collected a minidump with full memory as the application was sky rocketing on memory to 1.6 GB and then was throwing an out of memory exception. I found in the inner exception stacktrace that issue was coming from log4net ReaderWriterLock. I've disabled the log4net by using the suggested config: <log4net threshold="OFF" /> and then no exception any more.
The question is now if this issue is fixed in your latest version ?