There is a persistent misunderstanding frequently on this forum. Frequently it manifests itself around what users feel are hardware problems. In reality, what is being experienced are real radio frequency signal problems. They, almost always, are a function of the physical situation, and not drone hardware.
Most all drones require multiple signal links to function properly.
1. A bi-directional control radio frequency link between the remote controller and the aircraft. This works only when there is a clear air straight line path between them. Metal objects rock, dirt, and water reduce or kill this transmission. Water is in trees and most other above ground greenery.
2. A uni-directional radio frequency download link for the video feed from the drone.
3. 6 or more uni-directional downlinks from the GPS satellites.
All of these signal paths are effected by the conditions defined in point 1. Clear air direct line paths are required for all. Since each path has different radio frequencies used, and different signal strengths, the impacts vary.
In addition, these signals are impacted by other radio frequency signals hitting either the remote controller or the aircraft, or both.
The physics of all these radio frequency signals makes them weaken by a ratio of the distance between the source and reciever. If you go 2x as far the signal weakens by a factor of 4, a 75% loss. Add this to the problems caused by various physical objects.
Parabolic antennas and signal boosters help on this problem, but can’t help the signals attempting to penetrate objects in the straight line signal paths.
These drones are very complex systems, and without some understanding of these control systems, the pilot jeapordizes his drone’s safe flight. Settling the proper RTH altitude taking into account all the RTH issues (RTH reference altitude, terrain altitude changes, trees and other structures) is the only fail safe precaution available. Note that it will NOT help with a loss of GPS signals. GPS signal loss can only be resolved if you have enough control to get the drone into some kind of GPS signal clearing, usually a climb above whatever obstacle you have encountered.