The Twitter Card Validator is showing this warning for the linked post:
WARN: The image URL https://forum-test.blendernation.com/uploads/default/optimized/1X/236bbbe9fa50f882fc710f078b22276a6cb3b974_1_690x483.jpg specified by the 'twitter:image' metatag may be restricted by the site's robots.txt file, which will prevent Twitter from fetching it.
Testing this meta topic however looks good on the validator.