First thing that comes to mind is that you have hardware acceleration or Maximum Render Quality turned on during export.
Try without those.
What format/CODEC are you Exporting to, and what are the settings?
Thank You Jim. It appears that maximum render quality was checked in both Premiere and in Media Encoder. Just for knowledge purposes, is there a reason why this option does this and where it would be practical to use this option?
According to Adobe, here's the "why".
See here to get an idea of why compositing in linear color is important:
Seems many users, myself included, have differing opinions, though.