I've noticed with Alpha Vantage that when I am retrieving data for a list of stocks, occasionally the response will have an empty body.
- Are you having this error for the same stock tickers each time you fetch data, or is it happening for different tickers each time?
- What does the response body look like?
- When did the problem start? Has it always been like this, or is it intermittent?
It seems to be a bug on their end, and it seems to follow a period of 500 server errors to the effect of "Heroku App: Application Error". It doesn't happen every day, and it also doesn't happen for the same stock ticker each time I fetch data.
In short, it's a server-side bug. But hey, it's a free service and it's usually pretty great.
Since the error doesn't happen for the same stock each time, I added a retry feature, and that results in a mostly-complete set of data on days when the service is buggy.