I have a large multi-site install load balanced using a Flexible Load Balancing setup.

I am subscribing to the PageCacheRefresher.CacheUpdated event in the ApplicationStarted event of my ApplicationEventHandler as follows:

protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
{
    PageCacheRefresher.CacheUpdated += PageCacheRefresher_CacheUpdated;
}

private static void PageCacheRefresher_CacheUpdated(PageCacheRefresher sender, CacheRefresherEventArgs e)
{
    if (UmbracoContext.Current == null) return;

    LogHelper.Info<EventHandlers>("Page cache refreshed.");
}

Both servers are registered in the umbracoServer table server correctly and the umbracoApplicationUrl is set to the primary domain for the site in the umbracoSettings.config file.

Changes are published on Server 1 fine and the PageCacheRefresher.CacheUpdated event is fired on the master. The cache instructions in the database are processed by the slave server but the PageCacheRefresher.CacheUpdated event does not appear to fire on the slave server yet the lastsync value is updated and so is the umbraco.config cache file.

Any ideas what might cause that to happen?