My issue is that twitter card image is not shown as it is stated in title. But I think that I know what my problem is (robots.txt need to be fixed) and now I just waiting when it will be updated by Twitter. I decided to create this post to ask Twitter developers to enhance Card Validator functionality. It does not give me any information why my image is not shown (deprecated by robots.txt, too big, too small, different host, invalid certificate, ...). It will be good to add as a warning a reason why image can not be used by Twitter otherwise it takes too many time to find a real reason. Thanks in advance.
Troubleshooting steps tried already: