This occurs because the MakeStruct node will create a literal term for each input if nothing is connected. However, there is no explicit handling of some native 'noexport' struct types (e.g. FVector4) in FEmitHelper::LiteralTerm(), which then falls back to FEmitDefaultValueHelper::SpecialStructureConstructor() with a default struct value, but that API also does not have a special case for some 'noexport' types. In that case, LiteralTerm() currently assumes that StaticStruct() is valid for all other cases, which fails for any 'noexport' type that falls through.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-59565 in the post.