Anyone know why my iTunes will not import valid .mp4's and instead tries to gapless feedback them?

If it is processing gapless playback then it sounds like it did import them. Maybe you missed them. Check your recently added playlist to double check. Otherwise, I'd contact Apple.

Are these video files? Check in movies or TV shows.

If these are audio .mp4s, and they're not showing up where you expect, maybe the artist name and track names aren't coming through properly. They'll be in the recently added playlist, or at the bottom of your iTunes library.