I tried the config above in an Alloy demo site, and I get statements in log file.

Did a quick test where I wrote to log from start page controller:

private readonly ILogger logger = LogManager.GetLogger(typeof(StartPageController));

        public ActionResult Index(StartPage currentPage)
        {
            logger.Error("This is logging message from start page");
....

Mari,

I can also log fine from an Alloy demo site. No problems. I took the Alloy log config and used it in my site - no logging happens. 

It's so strange - the log file is always created. No issue there. I also have granted full control access to Everyone so there is no chance of permissions problems.

Today in messing with this, it started logging. I thought it had to do with changing the logging level to DEBUG as it was my last change. I changed the logging level from DEBUG to INFO, it stopped logging. I went back to DEBUG (I literallystopped the site, hit ctrl-z and started it again) and it still won't log.  It's just so strange. There is literally no rhyme or reason for why it behaves this way.

I also tried the very minimum logging config as shown here. It did start to work again so I began to add my other logging config lines 1-by-1 (like rollingStyle and datePattern). It stopps logging. I remove those, it still won't log.

Bottom line, there is seemingly no pattern for when it logs or doesn't. I'm beyond frustrated. The only pattern I can see is that this doesn't work on IIS Express. Our test and production sites log just fine with the exact same config. None of our developer sites log.

Does youe site by any chance have log statements in global.asax.cs? I've previously seen that that will cause log isses.

Have you tried upgrading EPiServer.Logging.Log4Net to the latest and greatest?

Are you using log4net directly or by Episerver's logging abstraction (private static readonly ILogger Logger = EPiServer.Logging.LogManager.GetLogger();)?

Sometimes log4net is not initialized correctly, and it fails to read configuration from EPiServerLog.config

Upgrading EPiServer.Logging.Log4Net usually solves the issue.

Mari, nope no logging in the global.asax.cs.

Dejan, we are at the latest for EPiServer.Logging.Log4Net, however, I upgraded log4net from 2.0.8 to 2.0.12 and I HAVE CONSISTENT LOGGING!

I almost can't beleive it's real, I've launched my local site a dozen times to be sure it's not goign to stop :)

Thank you both for the nudges in the right direction.

I would not give up :) What about if you run ProcessMonitor tool? Do you see that process is "touching" log file? I would also give a DebugView a try - to see if log4net is not emitting something on the debug output stream that might give you some clues what's going on..