Variants can have a "file" attribute that loads them from a file, and can have "name" and "frequency" attributes.
The loading order was unspecified, which means that the variant specific name can get overwritten by the file.
This happens with the briton fortress since rP24919. All three main variants get the same name, and because of how the engine calculates selections and picks variants, the first variant in the group with the matching name always gets picked.
We probably ought to check that variants don't have name conflicts, but at the moment we can simply make sure the actor-specific settings override the included file variant.
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https://wildfiregames.com/forum/topic/36427-old-brit-and-gaul-fortress-models-in-dev-version-24/?tab=comments#comment-416824
Refs: Phab:rP18054