Ok. So have I.
if you execute curl -v -A Twitterbot at the command prompt, does your page still show the twitter:card tags in the section of the page? Does your server return a 200 response code and a valid Content-Type header?
Answer: no.
$ curl - A Twitterbot -v
HTTP/1.1 500 Internal Server Error
Server: nginx/1.12.2
Date: Fri, 02 Feb 2018 15:05:46 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Cache-Control: no-cache, private
Vary: Accept-Encoding
548f
<!DOCTYPE html>
<html>
<head>
...
