I don’t know what has changed that caused this but you will have a lot of work to do to get it working again.
You should definitely back everything up before you start making changes.
Should have asked before, are any of these fields sub fields, like in a repeater, flex field or group?
Assuming the answer is no.
You would need to change the field name.
Then you would need to find an replace all occurrences of the field name in the database in the _postmeta, _termmeta, _usermeta and _options tables. Once you have done this you’ll need to update all of the ACF function calls to use the new field name as well.
In the meta tables this means replacing the ‘meta_key’ values
"{$old_field_name}" => "{$new_field_name}"
"_{$old_field_name} => _{$new_field_name}"
The options table is more complicated and if they are sub fields that gets even more complicated.
