Yes, that does clear thinks up a bit. I will take a look at this.
I have one suggestion though without looking too closely though. Usually when fields and field data disappear when saving a field group and other odd things like this it’s because you running up against the limit of the php setting max_input_vars.
Without duplicating a field your field group has 15,245 fields. I’d say that you’ve already increased max_input_vars before or you couldn’t have saved what you posted. You might want to increase it again. I find this plugin very helpful when developing large complicated fields groups. https://wordpress.org/plugins/wp-max-submit-protect/
Let me know if that does not solve your problem.
