In order if likelihood...
- Check it hasn't defaulted back to beginner mode in the app
- check you've got the height/distance limits set in the app
- make sure that Dji Go 4 is signed in with you Dji user login.
- within Internet wifi range for your tablet, sign out of Dji Go 4, then sign back in again.
- check your location on the map and make sure it doesn't think your in a nofly area, or in China!
- all else fails, connect the I2
aircraft Via USB to DJI assistant 2 and do a reset to factory defaults. Sometimes when it does an update it doesn't always read the stored option values back in correctly and a reset helps clear them.
If it still doesn't clear up, then final suggestion is to try a firmware refresh via Assistant 2.
Hope one of those helps.