The RTH was at 30 metres. Distance out was about 200 metres. Sorry, not sure what "the Phantom had signal from the angle, cut the line the pitch of the Phantom changed and you lost signal?" actually means. Would you mind asking me that question again, in different words, and I'll answer it?
It was a pretty straight line out and back. Should have been the simplest flight ever recorded. Let me think. Flew out. Dropped fishing line. A few hiccups on the way out, i.e. fishing line very briefly snagged but didn't seem to bother anything, resumed course. Time to drop the line. Probably at 20m. Line doesn't drop. Motor overheating message appears. Line drops, message stops, low battery message starts. Hit RTH as I trust it to not make any dumb mistakes more than I trust me with battery low. It then flies roughly back towards the coast, but not at me. RTH set at 30m, but drones flies over my head except North of me, and climbing. Not responding. Flies past the coast into the neighbourhood. Climbs to 184m from memory and perhaps 200m past me (at a guess).
Second low battery warning starts, drone not responding. Switch to "ATTI mode". Occasionally, it responds to my direction. Full video still available. Get it pointed back at the ocean, not wanting it to die 184m above houses. Try to get it to descend. Mostly it ignores me but from time to time a signal gets through and it starts to move. That is how it appears to me anyway. I have my fingers on "forward" and "down" so hard that I am surprised I didn't snap off the controls. It does seem to be moving that way. I am hoping it makes the ocean and I lose it, rather than plummeting through someones roof. Heart rate goes to maximum.
Can see through the camera it is heading the right way. As it gets closer to the beach, video stops broadcasting. Then resumes to show a very close up of a young family and their dog on or close to landing.
Miracle, it makes the beach, with a foot left of altitude, battery goes to zero, drone lands after a fashion, perhaps 500 metres from me. Maybe it lands and battery goes to zero at the same time. Heart rate also gone to zero.
Started with 100% battery. Ended with 0%. P4 Phantom Pro V2, owned it for maybe 6 months. Next day, (day after actually as I had to drive home plus wondering it is safe to fly, or whether the thing would just fly off, in an area with less margin for error). I replace the battery, take it for a test flight, 100% perfect.
This has happened to me twice. And not happened to me hundreds of times. Seems a certain set of conditions might come together to cause it but I am struggling to find it.
I am trying to thoroughly answer the questions and hope I am in the correct forum. Apologies if I am not, and apologies for a long post. I am not pushing any point of view, just trying to figure out what is going on. Perhaps it is pilot error, but I have been at this for a while, and I spent almost an entire battery trying to recover the drone from the most basic flight you could design.
I read something just now about the sensors not working properly around sunset. This was around sunset. The time before, was in the middle of a bright day at a completely different location. Equally heart stopping but had still battery left when I got it to land, near me but not at the RTH point.
I have been flying Phantoms since there were Phantoms. I have a Pilot's Licence. I might be stupid, but I am not an idiot

. This is too scary. Don't want to kill someone and go to jail because "it was sunset". All helpful suggestions welcome.
Also realise now I have to learn how to analyse logs, which I haven't looked at before, because, well, why? Because it was stressful enough that my recollection above is probably mostly correct, but wouldn't surprise me if I don't remember everything precisely, especially after my heart stopped.
Thanks