Maybe I'm stating the obvious here, but it sounds like a font activation/deactivation issue. Or, more specifically, a font failing to activate when the Premiere Pro Sequence is handed off to Adobe Media Encoder.
In your Premiere Pro Sequence, are you using a system font, Adobe font, or other 3rd party font?
I'd try two things:
First, export using Premiere Pro rather than Adobe Media Encoder. If you haven't done this before, just click the Render button instead of the Queue button when you're in the Export Settings dialog box (having set your Format, Preset, and location as needed). Hopefully, the Sequence will export completely by ramaining in Premiere Pro.
Second, if using Render instaed of Queue still results in a failed export, remove the font dependencies from the Sequence by exporting your Graphics as PNG files (most likely with transparancy) and then replace each Graphic with it's corresponding PNG file. Maybe do this in duplicate Sequence so that you always have the Graphics to edit later if needed. That, or place the Graphics in a higher Video Track and then disable those clips (Clip > Enable from the Clip upulldown menu).