This is what I did to get my Galaxy Tab S2 to work with my Spark:

1. Enable Developers options in tablet
2. Set USB configuration on tablet to RNDIS (USB Ethernet)
3. Power off the tablet
4. Power on RC and Spark like normal
5. Put one end of the OTG cable into the RC first, and then the tablet
6. Power on your tablet and DJI Go 4 should automatically launch

Video Caching is also a problem becuase it uses up your device's CPU & RAM that should be used for the live feed.
To disable video caching on any Android device for DJI Go 4 follow these instructions:

1.Delete DJI GO 4 and reinstall it.
1. Enter the app without connecting to your drone or RC
2. Cick Enter Device
3. Cick Enter the Camera View
4. Go to General Settings (It is the three dots icon)
5. Toggle off the Cache Locally when Recording option
6. Press the dji symbol on the top left to exit and connect to your drone normally
This should only need to be done once, and once you've done it say goodbye to lag!

Hi. Thank you for sharing your tips and suggestion with our Spark. This will a lot of Customer here in DJI Forum. If there is any help needed, please don't hesitate to reach us. Thank you and fly safe.

In A cache in number 5 , will only disable audio recording not video , if you want suspend video recording set your largest video cache capacity to 1G  and it will stop recording video when capacity is reached , just start the recording before you take off

At least for me on my Galaxy Tab S2 it says Cache Locally when recording.

Remove DJI Go 4 & any dji directories on the storage card.
Install DJI Go 4.
DO NOT CONNECT to SPARK or the RC.
Load DJI Go 4, enter camera view - settings & turn off local video cache.
Now connect to Spark & the video cache should be off.
Repeat the process to turn the video cache back on, but obviously leave as default (on?) or select as required.
Good luck.

Sparkz71 Posted at 1-29 04:03
Remove DJI Go 4 & any dji directories on the storage card.
Install DJI Go 4.
DO NOT CONNECT to SPARK or the RC.

Thanks for that extra step, I forgot to include it.