Part 107 UAS pilot reported that while conducting a preprogrammed flight with a UAS; a lost link occurred and the UAS did not return to home. The UAS was lost and not recovered.

Narrative

Took several advanced students to Park in ZZZ do capture some aerial photos for their portfolio. Following their flights; I took the ANAFI USA to demonstrate its autonomous mapping capabilities using the PIX4D application. I had updated all the software at the classroom prior to starting the trip. On site; after calibrating the compass and IMU settings I set up a simple mission selecting appropriate altitudes and obstacle clearances (200 AGL in that area). The other class members and I discussed and checked the flight area for possible bystanders and felt confident that we would pose no hazard to persons or property. It was a fairly short flight plan. I believe it was less than a 12 minute flight to capture a small map.So; about halfway through the autonomous flight the controller lost connection with the drone. No problem; I thought since the return to home function should have brought the drone in a straight line back to the home point. I did select manual return to home but; of course; without contact between the controller and the drone this was ineffective. I waited 20 minutes with increasing anxiety before concluding that either it was a fly-away or a collision. The students and I searched the planned flight area and were unsuccessful in finding the aircraft or aircraft parts. After the foot search we returned to the home point just to check if the aircraft had returned but with no success.I can't say how far away the drone was at the last point of connection; but it could not have been more than a 1/4 mile away. I was distracted by the 'loss of connection' indication on my controller and my subsequent efforts to manually command return to home; so it is likely that at this point I lost visual contact with the aircraft. Unlikely as it may seem; I can assume that this was either a flyaway or there was some strong interference in that area. Either way; it is likely that the aircraft struck a building or other obstacle. The other class members had not experienced interference and that evening I received reports from other operators in that area affirming no unusual interference. I have experienced previous loss of connection issues with the ANAFI USA aircraft but recovered the drone by searching or; in some cases; the return to home function worked.I am distressed about this incident since an uncontrolled aircraft does indeed present a hazard to people and property. I might have mitigated this event by not flying in downtown ZZZ. A flyaway in lower density populated areas would be far less likely to present this hazard. As far as human factors; I was overconfident in the return to home feature and under concerned that a flyaway would likely impact one of the tall buildings surrounding the flight area.