To me it sounds like a lack of performance/speed.
I am not fully sure which is the latest Android 7 version for FP2.
Initially there was a problem with .h264 hardware acceleration which meanwhile should be solved.
Maybe check if you have the most recent Android version for FP2.
Have you also played back the file locally saved on your phone or is it always streamed over the net with your FP2?
This could reveal problems with your network performance.
Of which type is the video format (.mp4?)
Afaik Gallery’s internal player is not operating smooth causing videos to stutter even on other phones (LG G4 Android 6).
VLC (MXPlayer) should perform flawless with any audio/video type just as on my FP2.
MXplayer offers several different ways of playing back media files using software/hw decoding by option.
But in general FP2 is potent enough to play back even uncompressed .ts files without stutter.