🚀 go-pugleaf

I'm using FM 8.0p277 on XP
No third-party tools.
All my dita files are broken down to the topic, concept, task, reference element level.
I'm now building an FM chapter from nested maps.

Problem
When I build an fm document from a DITA map (DITA / Build FM Document from Dita File),
the third-tier topic elements and their concept and task sub-elements (built from sub-sub maps) do not appear in my final FM document.
An error message briefly appears: "FM document generated from DITA Map, but with errors. Please refer to console for errors."
(I can't find this console.)
The FM document is built, but with missing elements.

For instance:
I build a mini map C: with topicrefs to one concept, and one topic element wrapped in a topicref to a topic element (Turning off the machine).
(This becomes a sub-section of my chapter.)

Then I build an intermediate map B: with topicrefs to several concept elements and task elements, plus a topicref to mini map C, all wrapped in a topicref to a topic element(Safety Features).
(This maps a heading 2 level section of my chapter.)

Then I build the top map A: with topicrefs to four intermediate maps, including map B (linked to map c), these are all wrapped in a topicref to a topic (Saftety Topics).
(This becomes my Chapter fm document.)

Problem:
Everything comes in at the right order, except that the information from map C is missing.
FrameMaker 8.0 does not seem to be able to pull in the third-tier map's topics. (Three nests of mapped topics.)

Is that right?
Do I need to give up the idea of breaking info down to the lowest topic, concept, task, reference, and making these third tier little mini-maps?

Note: each mini and intermediate map build into FM documents just fine.