I see you are using Safari. While we investigate, can you try a different browser such as Firefox or Chrome?
Are you running AdBlock (or something like that) on the browser that you’re not seeing the Send button on? That might explain it, especially if you have opted to Disable Social Media Buttons.
If you do a web search for "adblock share-button" you will see a number of postings about this issue with buttons missing from other sites.