Log4Net only logging when browsing from localhost - asp.net-mvc

Question

I've used Log4Net in multiple applications for a while. It has been working fine, but recently I noticed that the applications were suddenly not logging anymore. Turns out this issue is the same for all my applications, and they all suddenly stopped logging some months ago. The strange thing is that the logging works when I access the applications directly on the server (http://localhost/myApp), while nothing is logged when I access the application from another PC. My first thought was that it must be related to file/folder permissions, but allowing "Everyone" (Windows user group) full access to the log folder did not help.
They are all ASP.Net MVC 4 applications running on IIS7 (Windows 2008 R2 Enterprise OS), and the application pool is using "ApplicationPoolIdentity". Log4Net version is 1.2.10.0 and I am using a custom CompositeRollingFileAppender. I thought it may have been something wrong with the custom appender, but the problem remained the same when I tried switching to the standard RollingFileAppender. I've seen the issue on multiple servers.
Has anyone seen something similar? Please share your thoughts, as I cannot see why there should be any difference in accessing the applications locally or remotly.
Here is the log4net section in one of my applications' web.config:
<log4net>
<appender name="RollingFileAppender" type="[mynamespace].CompositeRollingFileAppender">
<file value="Logs/ApplicationLog.log" />
<appendToFile value="true" />
<rollingStyle value="Composite" />
<maxSizeRollBackups value="20" />
<maximumFileSize value="10MB" />
<datePattern value="_yyyy-MM-dd" />
<staticLogFileName value="true" />
<preserveLogFileNameExtension value="true" />
<layout type="log4net.Layout.PatternLayout,log4net">
<param name="ConversionPattern" value="%utcdate;%property{ErrorCode};%property{Severity};%property{ErrorName};%property{Module};%m%n" />
</layout>
</appender>
<root>
<priority value="ALL" />
<appender-ref ref="RollingFileAppender" />
<level value="Warn" />
</root>
<logger name="NHibernate">
<level value="OFF" />
</logger>
<logger name="NHibernate.SQL">
<level value="OFF" />
</logger>
</log4net>

Answer 1

Turns out the issue was not directly related to log4net, but to the way ASP.Net MVC3 and newer handles exceptions by default. Some months ago we updated our applications from MVC2 to MVC4, and because of this code which is executed by default from global.asax.cs.Application_Start(), it "bypassed" our exception handling module when CustomErrors where set to RemoteOnly or On:
public class FilterConfig
{
public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
filters.Add(new HandleErrorAttribute());
}
}
This thread put me on the right track. I ended up removing the filters.Add(..) line, and now it seems to be working fine!