My S2 9.7 had both DJI Go4 and Litchi installed on it. It would only default to Go4. After reading about USB configs and startup procedures, still Go4 would be the default every time I restarted the S2. I deleted Go4 as I fly mostly with Litchi for way points. Now, when I restart the S2, with the proper procedure I'll get a rapid flashing statement asking me to set litchi as default and 'OK', which I tap only 'ok'. Eventually it connects and loads the app. Now, with very limited time since then it connects to Litchi every time with the statement not flashing anymore. Have not reloaded Go4.
Flying with Litchi with the S2 I'm getting about a half sec lag and the screen gets pixelated. Had no problem on S7 Edge.