from DJI's forum (edited):
IMPORTANT ! HERE IS HOW TO EASILY FIX THE LAG ISSUE!
1: Reset you tablet to factory default (Settings→Backup & Reset→Factory data reset.)
2: Install Zapper Task Killer and run it.
3: In Zapper, select All processes and Kill All.
4: On the tablet, go in Settings→Apps, manually select all apps and disable notifications for every single app you can do so.
5: Open the Play Store app, go into the Settings by clicking the 3 lines on the top left corner and disable automatic updating of all apps.
6: On the tablet, go in Settings→Developer options and set “Logger buffer sizes” to 256K (Not sure if it's important but seams to have helped for me).
7: Reopen Zapper again and Kill all processes again.
8: Kill all processes again using Zapper(Yes why not twice !)
9: Power up the drone.
10: Plug your remote, and turn it on.
11: Start the DJI app and log into your account.
12: Enjoy lag free flights…
Also I advise you set ALL animation options in the Developer options to OFF to improve performance even better…
Note: since these settings will affect regular use of the phone or tablet, it is best to use a dedicated phone or tablet for drone control, not your regular device.