What Does it Mean?
The URLs have some Twitter card tags on the page, but are missing one or more of the required tags.
Twitter Card tags are a standard similar to Open Graph, but are only used for Twitter. These tags provide rich meta data about a page frequently used to created "cards" about a page when a link is shared Twitter. These cards may contain an image, description of the page, a site name, and other data that is much more visually appealing than just a simple link.
Twitter tags are <meta> tags with the name attribute set to a list of supported types with the prefix "twitter:". Here's an example of the "title" Twitter Card tag:
<meta name=”twitter:title" content=”Amazon.com: Online Shopping for Electronics, Apparel, Computers, Books, DVDs & more” />
There are five recommended Twitter card tags: "twitter:card", "twitter:site", "twitter:title", "twitter:description", and "twitter:image".
Why It's Important
While technically only two tags are required ("twitter:card" and "twitter:title"), you will not get all the benefits from Twitter Cards by sticking to these minimums. The card may display, but it may not be attractive enough to attract the maximum potential clicks that a fully-developed card would.
While Twitter tags do not directly influence organic rankings, they will likely have an impact on the click-through-rate of social shares of this URL. The more people share and visit a link, the greater likelihood web sites will link to this URL as well, thus helping to improve organic search rankings.
If a corresponding Open Graph tag is present on the page, Twitter will try to fall back to this for missing data. So you may not need to implement this if you already have Open Graph tags.
How To Fix
Look through the URLs and add the five recommended Twitter tags to these pages:
twitter:card: Set the value to either “summary” or "summary_large_image"
twitter:site: The Twitter @username the card should be attributed to.
twitter:title: A concise title for the related content. Keep it to 200 characters or less. No need to include keywords, but make it interesting so that people want to click it.
twitter:description: Similar to the meta description on the page. Not shown on mobile devices, but truncated to 3 lines and shown on the web. To play it safe, try for 200 characters.
twitter:image: URL of a JPG, PNG, WEBP, or GIF image for this page. The aspect ratio should be 2:1 and a resolution at least 300px by 157px but no more than 4096px by 4096px. Try to keep the file size to 1MB or less.