The error message in the logs is:
This error message is cryptic and does not tell us anything about the true reason. Which is that for StructuredRecord, the schema must be read from one of the dataset properties, and the Explore service has logic to do that. But it only calls that logic for ObjectMappedTable. (ExploreTableManager.java:160):
This is not sufficient. Perhaps we can say, anytime that the type is StructuredRecord, it must call this method. Not sure what is right.