Avid Media Composer Not Importing MP4s
The problem is that your video files are encoded using variable frame rate, which is typical of screen recorders. Premiere is trying to kind of grunt through it, but on longer clips you'll probably notice that you get some synch drift with the audio.

Transcoding for a constant frame rate file, either going back to H.264 (where you might lose some quality) or to something more editing-friendly, like DNxHD. ffmpeg can handle this pretty easily. Just be aware of the limited number of video formats that DNxHD supports.