On error, log not just the HTTP error code but any messages from the remote server as well.

[nrvale0]

I have a set of feeds which fail periodically. As has been mentioned in other Issues, it seems like it might be a result of CAPTCHAs. It would be excellent if, on fetch failure, elfeed logged not only the HTTP error code but also any messages from the server. I suspect that would provide enough context to be able to discern CAPTCHA-related failures from other root causes.