I had several similar situations:
At the start there was no error message although a significantly poorer signal was present and less satellite were visible because tall trees obscured the satellite.
At an altitude of 100 meters and a distance of 100 meters, at "best reception conditions", I got the "weak signal" warning, then the I1 independently turned from GPS-Atti to ATTI.
In the flight area there is neither industry nor is a settlement
I informed DJI Europe about this "error / firmware bug"? including "heathydrones" flight log evaluation but DJI denied a "firmware bug"
I got a the following answer:
(Answer is translated from German to english with google translate)
"No, that's not a mistake. This is by design. The sensor data are checked sharper by external interference. The copter then switched to Atti mode and so on are the pilot control. Thus a safe flight is ensured, provided the pilot dominates the aircraft. a loss of control is not equal to more dangerous. the copter checked doing a little more than just the number of Satellite. "
Original Text
"nein, das ist kein Fehler. Das ist so gewollt. Die Sensordaten werden schärfer nach externen Störeinflüssen geprüft. Der Copter schaltet dann in den Atti Modus und übergibt damit den Piloten die Kontrolle. Somit ist ein sicherer Flug gewährleistet, vorausgesetzt der Pilot beherrscht das Fluggerät. Ein Kontrollverlust ist ungleich gefährlicher. Der Kopter überprüft dabei ein wenig mehr als nur die Anzahl der Satelitten."