thanks @andypiper for looking into this.
Impact is on sharing articles on twitter as sometimes images from article do not appear instantaneously on twitter and take some time before it appears on twitter, which is not a good user experience.
In order to check the issue when we try to preview card on twitter card validator, some times it works and some times it fails and give request timeout error.
Please note that we are using same article web page and trying to preview multiple times, repeatedly within same minute.
Even though it was cached and response time and TTFB are in range of 300-600 milliseconds.
Can you please suggest on causes and how this can be fixed.