Why is Discord only showing parts of the notification?
Discord collapses messages that contain links if link previews are disabled, even when the message itself contains plenty of other content. That's why some Oh Dear notifications show up looking empty or truncated in Discord.
The fix is a Discord setting, not an Oh Dear setting.
In Discord, go to User Settings > Text & Images and make sure Show website preview info from links pasted into chats is enabled.

With that option on, our notifications render in full:
With it off, they look like this:

The setting is per-user, so anyone else in the channel who's missing notification content will need to toggle it too.