Nobody can tell you anything without exact system info or other technical details. Sorry, but spitting bullet points is not useful. You have to provide exact comp settings, render settings, version of AE, system info and all that good stuff.
comp 1920 x 1080
new PC i7 16gig GTX1070
using the Media Encoder.
What effects are you using? What is the format/codec of any assets/footage you are using? What are your render settings in Media Encoder?
AE Pixel Sorter, MP4
Try using Adobe Media Encoder to transcode the footage you're using in your composition into a production codec like DNxHD, Cineform, QuickTime with the Photo-JPEG codec, etc.
Did you ever sort out this issue? Did you transcode the file as suggested? Please let us know.