Hi Jeremy,
I did a quick Google search and it seems it's an incompatibility with the latest Cordova iOS version. It was working for us because we aren't using the latest version yet. We'll take a look to fix it in our main repo, we'll probably use the new version (not deprecated).
Meanwhile, you can just go back to a previous version of the iOS platform (3.9.1 is working for me) or maybe try this fork of the plugin that seems to include some bug fixes:
https://github.com/Telerik-Verified-Plugins/PushNotification
I created this issue to fix it in our repo:
https://tracker.moodle.org/browse/MOBILE-1494
Kind regards,
Dani