HTML Email sent from Meteor not showing up in iOS Mail

So I’m having an interesting problem. I have a multi-part email (an html template compiled using meteorhacks:ssr, and a text-only version) sent using the default Email package via Mailgun. The email itself sends without issue. If opened in a browser, android phone, Outlook, etc, the email comes in just fine.

However! If opened via the iOS email app, the body comes in blank. The heading is there, etc, but no text. I’ve tested this on multiple iOS devices, all are doing the same thing.

Other information: The HTML itself seems fine – I’ve sent it to the same email addresses via other services, and it works without issue. If the blank message is replied to or forwarded (by the iOS app or any other platform), those messages will show the message without issue.

So basically, it looks like something in the meteorhacks:ssr > Email > Mailgun toolchain is getting into an argument with iOS. Does anyone have any idea what could be causing this?

Template code on codepen:

Bizarre - maybe start cutting parts of your HTML email out bit by bit, testing to see if it will render properly after each cut.