It doesn’t happen that often, but it can, if you’re not careful…
You need to be aware when you create your Business Rules that if the logic relies on a field value and the field is NOT available on the form, the business rule will NOT work.
The solution is to make sure in the form designer that the field is available and visible – It doesn’t necessary need to be enabled.
If you need to hide it, you should do so in the Business Rule logic.