1. Add a constraint to QuestionnaireResponse like "qrs-2": "Repeated answers are combined in the answers array of a single item".

(QuestionnaireResponse | repeat(answer|item))
.select(
  item.where(answer.value.exists())
  .linkId.isDistinct())
{{.allTrue()}}

2. http://build.fhir.org/questionnaire-definitions.html#Questionnaire.item.repeats states 

> An indication, if true, that the item may occur multiple times in the response, collecting multiple answers for questions or multiple sets of answers for groups.

but per https://chat.fhir.org/#narrow/stream/179255-questionnaire/topic/Repeating.20answers.20to.20a.20top-level.20question/near/251593867, an question-type item will not repeat QuestionnaireResponse when multiple answers are provided.

This text should be updated to say something like: "An indication, if true, that a QuestionnaireResponse for this item may include multiple answers associated with a single instance of this item (for question-type items) or multiple repetitions of the item (for group-type items)"

—

Overall, the guidance for how repeated answers should surface (as sibling items, or as sibling answers within an item) should be made explicit, if we have expectations here. Ideally we'd formulate fhirpath constraints documenting when sibling items would (and would not) be allowed to have the same linkId, to prevent mistakes.