Hi, Michael

After some digging, I found a code bug in commit
3c623c26ae7d695746e05d8a2e16a67a6256b024 introduced by me and maybe
relavant to your report.

lisp/url/url-http.el:

  1319	(defun url-https-proxy-after-change-function (st nd length)
......
  1327	      (url-http-parse-response)
  1328	      (cond
......
  1360	       (t
  1361	        (url-http-activate-callback)
  1362	        (message "error response: %d" url-http-response-status))))))
......

When using url-http in eww and the above "cond" last clause succeed
(i.e. at first connecting to proxy response not HTTP 200), "url-http-activate-callback" will call
function "eww-render" which calls (kill-buffer), so the code next line
visit symbol url-http-response-status will cause the error: "Symbol¡¯s
value as variable is void: url-http-response-status".

This can be fixed simplely transpose that two code lines: