A few months back, on some developer machines, their local install of AppFabric was failing to populate the local AppFabric monitoring database. I wrote at length here the trouble shooting I went through - i.e. all the typical components were working as expected, services, sql agents etc.... and no errors / warnings were being logged.
The reason the monitoring events where not arriving at the monitoring database was because the ASEventSourcesTable (located in the monitoring database) was empty.
This table is populated when the AppFabric Event Collector service is started, and for whatever reason was not being populated automatically on the machines who were not logging (the table contains a list of the services that are hosted in IIS who are applicable event sources). To date, I still haven't figured out why AppFabric is unable to populate it on certain machines.
Using another install of AppFabric, where the ASEventSourcesTable was populated automatically, I manually inserted the missing rows into the empty ASEventSourcesTable, and boom - events start arriving in the ASWcfEventTables.
So, along with the usual places to check when you cannot see events in the AppFabric monitoring database, check to make sure the ASEventSourcesTable has been populated. So far I have only seen this occur on Window 7 machines.