Provided that you used Litchi's settings page to ensure that the waypoint mission continues after signal loss, and provided that the Litchi mission you designed does NOT show a flight time that is greater than the average flight time of your...
What you are missing is that the signal was completely blocked, so you couldn’t possibly have seen the drone, no matter how close. The blocked signal is what led to the loss of signal RTH.
You can still maintain clear Line of Sight (LOS) at 10...