@Jesca Bard - What you are describing appears to be the same as in the following post and apparently is the expected behavior with the wireframe objects at this time:

https://community.miro.com/got-a-question-ask-the-community-45/export-wireframes-1515

As @Kiron Bondale states in the above post, an interim workaround would be to use a third-party screenshot tool to capture the full wireframe object. As Kiron mentions, Snagit is one option and I personally use this as it has been around for a long time and has a ton of features.

Another solution I have recently started using for very simple and quick screen grabs of the browser window is the Miro Extension for the Chrome browser.

I’m not sure if once Miro add the ability to export the wireframe borders they will post in the Community forum Changelog Discussion category, but if you want to stay in-the-know, I would suggest going there and clicking on the big blue Subscribe button at the top right. You can also visit the Miro Changelog page from time to time too.

Thanks everyone!