I did some more research on this. It appears the the two different Blocked fields have different definitions in terms of allowed values and default values...
It looks like the CMMI.Blocked field in a work item only has "Yes" as an allowed value and does not have a default value. So, any work items created in a project that uses the CMMI template end up having a blank value for the Blocked field and can
only be set to "Yes" or left blank.
The Kanban.Blocked field in a work item, however, is defined as having both "Yes" and "No" as allowed values, with a default value of "No". So when a card is created, for example, the Blocked field is set to "No" can can be changed to "Yes" or left
I'm not sure if these differences are enough to cause the data warehouse refresh to have issues (as listed above) and I'm also not sure why you cannot recreate the problem (as I don't think we've done anything out of the ordinary with our TFS environment)...