Opening a video in Photoshop CC causing frame loss

Without knowing any details, one of the main reasons for frame drop out is that the computer is not fast enough to decompress the video on the fly.
There is another reason which is a setting, the fps determines how many frames will be used. If set too low you will get frame droppage. Too high and it is filling in the blanks with neighboring frames.
That said, when saving to gif, I wouldn't worry too much about it anyway. As you are at the mercy of the web browser playing the gif animation. It will determine the fps with no way of adjusting it.
So playing a smooth movie is pretty much out. But for generating short animations even at 15fps it is generally fast enough to create the illusion. Just don't expect anything above 30fps.

Without giving us any information on the video format, the framerate and how you converted from video to frames no-one can really answer your questions.

Dave