[Plugin: User Avatar] Avatar images not appearing in email?

Hi, we’re using this plugin for users to set up their Avatar on a site we’re building. We’ve built our own plugin that then pulls the Avatar along with other info from the user’s profile into some emails that get sent out to the users.

However, when the email arrives the Avatar image is always broken: no image shows. But if I use dev tools to grab the URL of the image from the email, then paste it into a browser tab, it loads just fine. Also, at that point, if I close that email (in Gmail) and open it again, the Avatar displays just fine! For comparison & testing we have a Gravatar in the same email. It displays just fine, every time.

Any ideas why this would be? And what we can do to get it display normally the first time the email is opened?

https://www.ads-software.com/extend/plugins/user-avatar/