Using a 3rd party app doesn’t void your warranty. If it did why would DJI create an MSDK enabling the creation of 3rd party apps?
The DJI warranty would not cover a mishap if it were CAUSED by a 3rd party app. I’ve heard of plenty of mishaps but they are all caused by either pilot error or pilot misunderstanding of a function. I am not sure I have heard of an accident CAUSED by Litchi.
If you have lost a drone and want to submit a warranty claim, DJI will not accept a Litchi log file to determine the cause of a crash or flyaway.
DJI Care Refresh only requires a broken drone and no log files.
DJI Fly creates a flight log file in the DJI file structure of your flying device. Litchi creates a flight log file in the Litchi file structure of your flying device. The two log files are different. DJI’s contains much more information than Litchi’s.