Datamart missing tables

This happens to me frequently, it's a nerve-wracking experience when it happens the first time.  It seems to happen when the source data is being refreshed.  In my case there are other dataflows that are sources for my datamart.  If they begin refreshing - the tables will disappear from my datamart until complete - however, executing queries on the emply datamart still works (oddly enough).  However, if the refresh fails for some reason - too often - then the table will not re-appear until the refresh on the dataflow is executed without error.  This can cause someone to panic and unnecessarily re-build their datamart (again) when it doesn't need it.  This is sometimes difficult to navigate the root causes because the datamart owner may not own the dataflow and has no visibility into what is causing the refresh failure.  Hope this helps someone in the future from going through what I had to do to understand it.