My video keeps glitching when I try to render it in Media encoder

Start by checking your hardware acceleration settings and update your system's graphics driver. For anything beyond that indeed much more info is required as per @Rick Gerard's reply.

Mylenium

My first guess, you have a corrupted MP4 as a source file in your composition. Without workflow, comp, OS, AE version, and system details, that's about all I can think of.