DJI has changed around their SDK and updated firmware to go with it. You might need to try 3.1.20 available here:
https://support.dronesmadeeasy.com/hc/en-us/articles/8160429529876-Installation
Or try 3.1.11 that some people are saying still works.
Also, please do the normal steps of power cycling everything and starting with a small mission to check the basics. If you are using Terrain Awareness that could be the cause and the issue has been addressed in 3.1.20.