I have a weekly survey running since June 2017.
If I download a weeks data as an Excel spreadsheet from the web interface, it has always contained a Weight column with the respondent weight.
However, for my surveys since the end of June, if I download the weekly survey with the API, the downloaded spreadsheet contains a Weight column, but it is empty. The early surveys conducted in June download with weights using either the web site or API.
Survey id 7y5cdnpprsjn4ie4tmlmwkvyne (publicly readable) is an example.
The problem here of course is that the data downloaded by the API are unusable without the weights.