awhile ago i synced through iTunes my phone which is an iphone 6plus. I just noticed that i have 101 videos showing on my MacBook but my phone only shows 86 videos? for some reason there are 15 videos on my phone that will not sync back to my iphone?? It shows invalid format or something as an error. No formats have changed and they were on my phone at some point so why wont they transfer back to my phone??