Part 107 UAS pilot reported a lost link and a fly away of the UAS. Pilot stated the UAS app indicated 'strong radio interference.'

Narrative

Around XA:15; my observer and I began surveying Phase 7 at Location X working from the north of the unit to the south. the mission was planned in Pix4D capture on an iPad. As the drone finished each transect; we walked to the start of the next so that we were always perpendicular to the flight path and the sun was always at our back. After the 7th transect; the drone's battery was changed and the mission resumed. It was around XB:00. As the drone approached the 8th transect; it lost connection with the controller. Both the observer and I lost sight of it at this point. My observer attempted to locate the drone using binoculars; but was unsuccessful. We waited 15 minutes for the drone to return as it was programmed to do but it did not. We traveled in our truck north on Location Y and then west on interceptor until we were perpendicular with the drone's last known coordinates and tried reconnecting. The DJI app said 'strong radio interference' and would not reconnect to the drone; nor could we see it unaided or with binoculars. A coworker double checked the original launch site in case it had returned (it had not) while we continued driving around the unit trying to reconnect. Ultimately; we were unable to re-establish connection or to re-sight the drone. Given its trajectory; there was no risk to person or property and it likely either hovered in place until it fell or continued west over the property. I will survey the drone's last seen location via airboat in the morning. There has been significant radio interference in the area as of late; but even with that the drone should have returned 'home' once its mission was complete. It did not. The distance between myself and the drone was close to a 1/5 mile; however it had already completed 7 transects without issue and within my line of sight.