Hi Carla,
It’s been so long I can’t remember how I got around it. The first thing to try is to delete all premieres cache, MCC, and preview render files associated with the project. Then reboot your computer. Open premiere, open your project and let it do its thing with recreating the preview clips (I forget what they are called), then create a new sequence in the project. Copy everything from the problem sequence and import it into the new sequence. Then export using premiere, not using Media encoder. See if that works.
If it does not, you could always increase the scale size of the offending clips to 100.1 percent and that should work fine it just increased my render time way back in the day because my computer was slow for even back then. I hope this helps 🙂