You have 2 issues:
- In the P3:
If the missing video is the end of your flight, maybe you didn't stopped the recording before turning off the bird. You can restore the unfinished video by putting the card back in the bird and powering it, it will close and finalise any unfinished video found on the card.
-On the tablet:
Maybe it is not enough powerful to cache all the video. Recording the live 720p video on the tablet requires a good tablet and it become worst when temperature is high. I personally don't enable recording on tab as I have a tablet not enough powerful and want to focus on keeping flight control capability at the best.