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I cloned your form and tried to make some changes. I was able to save it without any issues.
However, I checked the conditions and it looks like there are conditions with errors in them. This might occur when a field connected to the condition was deleted.
This might be why you received an error when you tried to duplicate some of the fields. I suggest you fix these conditions before you duplicate the fields, then try saving the changes.
Do inform us if you need further assistance,
Thanks. I will fix the conditions. This was a big help.