Log4net is a fail-stop logging system. Fail stop means that it stops logging on an internal exception and by design does not interact with the program flow. Knowing this explains you troubleshooting log4net isn't so easy. If logging fails, your program does not notice. You see a lot of questions about: why is my log4net logging not working? This article explains the basic troubleshooting and to most common solutions.
In most cases the first step is to enable internal debugging for log4net.