In some cases you may notice that video is choppy when playing back higher resolution videos that have been downloaded through the GoPro App and played back on a phone. Some phones can have a difficult time playing back high resolution video smoothly. If playback is choppy the actual video file is likely fine, it is just a playback issue on the specific phone and will likely play back smoothly on other players
As a workaround, you can try using 1080-30 or downloading the low resolution videos instead.
For more information, check out this article which has a chart displaying the resolutions that certain phones may have a problem with.