You know, I read something this morning that was very interesting in regards to declining range. It was something about 8 verses 32 channel communication. I'm paraphrasing here, but it said something about unlocking all 32 channels for better comm and range. Apparently the early Phantoms used all 32 channels that they are capable of for communications. Basically there were 32 different frequencies the drone could choose from, and if one was busy, or had a lot of interference, it would automatically switch to another to maintain communication. At some point, or at some Firmware update, the choice changed to just 8. If that is correct, it would explain the recent range loss. Apparently you could see the channels in the earlier DJI Go App by clicking on the HD ikon at the top of the screen. I tried to find that ikon, but it was gone. I'm assuming DJI removed it to prevent making the change.
Perhaps someone else could find more information and explain this further. YouTube has many videos about this.