When posting a tweet with multiple links, I found Twitter used the last link for the Twitter Card despite what the documentation says.
One of my posts was shared and it did not have an image for the Twitter Card. After I added an image for the Twitter Card, I had to clear the cached version on Twitter so the image would appear in tweets. This is how I cleared the cache and updated the image in the URL for Twitter.
Search tips for Twitter copied from tweet thread at https://twitter.com/TexanTruth42/status/996533468707414016