Can you share the related part of your XLSForm, incl. choices (of the 2 lists), please?
Did you check your form with the Online validator?
Did you redeploy the last version of your form and use this version in Collect?
Thank you! I solved it. The problem was that in the question there is a choice filter. For some reason, the choice filter wasn’t working in Collect but well in enketo. What I did to solve it was to assign the choice filter to a new calculate that pulls the answer that will be the filter from the first question.
It might help others, if you could share an extract or screenshot of the related part of the form, for the solution and for the problematic version, please.