There have been several threads about this issue on the forum. My P2V was doing this last year.
One time I had sent it on a Ground Station flight over some wooded property, where it was out of my sight and control for a few minutes. It had just come back into sight with about 50% battery remaining when the klaxon sounded and it started to auto-land right over some 100' trees. I was able to override it and steer to a safe landing. Had this happened a few seconds earlier, before I could see it and regain control, it would probably still be in the trees.
I sent it back to DJI in November for this issue. They replaced the battery and one motor. Not sure exactly how that fixed it, but I haven't had this issue since.