I've been having this issue, too. I went through the DJI chat thing, and it was useless. He asked me like three questions and then said I should send it back. Seriously limited troubleshooting. There was a video for a quick fix on YouTube which I tried, and it worked for the next 8-10 flights before having the problem again today. I did the fix, and took a long flight - worked fine and I thought I was good again until about 8min left, and there's the warning again. UGH. The only thing I can see that might be a common denominator is when the camera is looking down (or down-ish), and I try Spotlight or the like, and it has trouble following something close to directly underneath it. But that doesn't explain why the problem resurfaced tonight on a post-'fix' fireworks flight where I was never looking downward.
I'm really struggling with having to send this drone back to DJI, as it's going to cost me money not having it.