It looks like you're trying to add an existing question to a collection which will cause problems for any existing forms of this type. Please try giving that field a different question user code which should fix the issue.
Error with new form setup: 'Historically this question does not belong to a collection, it cannot be added to a collection'
In this article, we explain why Mosaic shows an error when adding a question to a collection if it wasn’t historically part of one.
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Written by Yusef Abulaynain