I'm currently experiencing this issue where mp4 footage that I import into premiere is being distorted in playback, even if I render the timeline. This is footage recorded with quicktime screenrecorder then converted from .mov to .mp4. I do this all the time and have never experienced this before. The main problem is it also shows up after I export the footage. I'm not sure where to even begin with trouble shooting this. I would really appreciate some help with this.
Oh man, I've had the exact same (or at least very similar) distortion issues when working with files that have been touched by Quicktime. Typically this is iPhone footage that has been trimmed on someone's laptop.
Anyway, there's likely a better fix out there, but what I've been doing is transcoding (or compressing) with Handbrake before importing into Premiere.
I use Handbrake because Media Encoder generates files with the same distortion. Just be sure to set your framerate to CONSTANT instead of PEAK. Hope this helps!