Movies will not copy over to iPhone

I'm on 10.2.2 and the current version of iTunes, with the problem occurring on an iPhone 5, 5s and 6+ (running the current version of iOS).

I'm getting really frustrated trying to get movies (and music) onto these phones. Sometimes it works, most of the times it doesn't. I have the manually manage music and videos checked (iTunes Match is off). I'll click on Movies or TV Shows in my device, click Add To, drag the files and click done. Nothing. I get the grayed out circle next to all the files. If I go ahead and click the Sync button after that, they still won't copy over.

Sometimes, if I restart my computer and phone it will work, but usually it doesn't. I tried toggling the 'manually manage' button. The video files ARE compatible (they've transferred over in the past), so that's not the problem. Some of them are purchased in iTunes.

I'm trying not to rant on how much I hate iTunes 12. But this is driving me crazy. There's just no good way to get videos on a phone. Especially with this problem.

Anyone have this happen and know a good solution?