You cannot depend on instance ids, they are not guaranteed.
declare("Device.X_TP_GPON.Link.[]", null, {path:4});
You’ve told GenieACS that you want 4 instances, but don’t specify the data for the 4 instances. Please see this link for the syntax.
Your best bet is to build up the config you want on the CPE and replace the built-in config with that. Trying to create interfaces on the fly is going to be fraught with issues.