cannot interpret or replicate PBI refresh error "Model object names must be non-empty"

this error has crept in my rather complex model tapping in to many spreadsheets.  PBI lists a dozens of queries with this error when I try to refresh from PQ. 

> no PQ query is showing faults, no measure is showing faults   

> I actually do not understand the error, and could not replicate it in a blank PBI model and simple Excel data sheet (image below)

> I see no commonalities in my erring queries, such as the act of promoting headers (some link to an Excel table not a sheet, without promoting headers)

> I tried copying each query to a blank database, hoping at leasst one of them would generate the error.  None did.  (when you copy a query, all preceding queries and parameters are copied too).

Can someone generate the error in a simple example, or point me to such an example?