Slo-Motion video capture on iPhone6

Hi

I am having trouble with accessing the slo-motion videos shooted in near past. When I go back and open them from my gallery the buffering kinda processing keeps happening and the video doesn't play. I am currently using iPhone6 16GB with an iOS 8.3(12F70). Sometimes they do play also. I am really puzzled as to why this is happening...is it the latest update I did or the memory space available to play or what. please help me resolve this.

regards,

Natch8.