I have not seen this exact same issue here unless I missed it. I have my RTH altitude set at 140 feet which is higher than anything in my flight area. Yesterday I was flying and my battery level warning came on. I had lost sight of the drone in the clouds but I knew the general area and it was a field. I was not 100% sure where it was so I lazily hit the RTH button. I was at 200 feet and the drone started dropping as it should, but it kept dropping until it stopped at 40 Feet. I manually flew it home and checked the RTH, the Altitude was at 40 Feet. I know I did not change it because most of the trees in my area are 100 feet tall. So how did this get changed????