You may have set the variable that is not return in the response data. Check it in the response data and make sure your response has right data.

For Instance:

request = https://postman-api/%7B%7Bid%7D}
response = {data: {key1: 1, key2: 2}}

On Script Tab: you might be setting the variable to the unknown variable.
pm.environment.set('id', id)