If a page "Origin" contains an ask query 1 with format=template, template=Nested1, and Nested1 contains an ask query 2 with template=Nested2, and Nested2 contains an ask query 3 with template=Nested3 (which contains no further ask-query, but simple display), the query fails.
We tested, that both the sequence:
Origin-with-ask-query 1 + Nested1-with-ask-query 2 + Nested2-with-ask-query 3 (with format changed to table instead of template, making Nested3 unused)
Nested1-with-ask-query 2 + Nested2-with-ask-query 3 + Nested3-simple-rendering
works fine. This seems to indicate that it is not the number of ask-queries (which is the same in both cases), but the depth of nested ask-template-formats is limiting.
The described depth of nesting is necessary if a result shall be presented with two levels of subheadings (grouped by factor 1, then grouped by factor 2).
I have not found this limitation documented and believe it is unexpected low. Some limitation of levels of subheadings may be reasonable, allowing only one level of subheadings in a report seems over-constrained and I wonder whether this is intentional or a bug.