I was guessing that the issue may be caused by me not having an explicit iPad version of the app. I now have an iPad version of the app but the issue still exists according to my users, it is working fine on my test devices however. Can anybody tell me if it may be an issue with development vs production iCloud containers? I have pushed the schema to production already but the issue persists...

@deeje Are you asking if the users enabled it on their iCloud account? If so, I'm guessing yes but I don't know for sure. The app itself uses iCloud Drive to save documents that can then be viewed between all devices, so yes the app has iCloud Drive enabled.