Video recording stuttering, how can I fix it?

Hi further to a post entitled Sd card ,I'm now finding it's probably a fault with the phone which is why I'm posting again and asking for feedback .I hard reset the phone and didn't restore from backup and the video is still pausing momentarily on playback,also there is a slight lag when pressing the record button ,as well as this I've noticed that sometimes it won't playback the video but the screen remains black and I have to press the back button to "retrieve" the screen .Ive had the phone less than two weeks so I'm
guessing there is an issue with the phone and I need to get down to the carphone warehouse and change it .The camera itself is excellent with clear photos and no lag,has no one else had video issues thanks

There is a bug the second to latest insider release mentioned about video and SD card. Dropping frames. Not sure if that's related and it's a software issue...

I'm saving videos to the device as I was wondering about that and also I'm not on the insider just the latest107 release