Hi @ABC6NEWS.
The “loading symbol” you are seeing is actually the character counter. It changed when Twitter switched from 140 characters to 280 characters. The more characters you use, the more the character counter fills up. This is on both desktop and mobile versions of Twitter.
To solve your issue with the Card not appearing - the preview of the Card will not appear in the Tweet composer unless on mobile. Since you’re Tweeting from a web browser, the URL Tweeted will automatically be rendered to a Card once sent.
I posted this Tweet with the given URL and the Card rendered perfectly fine.