Actually, instead of RC Calibration, I should have said that I performed a Vision Positioning System Calibration this morning, done with DJI Assistant 2. I've been on a chat with DJI for the past hour with no luck. They had me calibrate IMU and RC, but no success.
Thought I'd try another VPS calibration, so this happened...
When I try to calibrate with DJI Assistant 2 on my desktop PC, first of all, as I enter the 'Calibration' screen, audio of a man speaking what I assume to be Chinese starts playing, and then starts playing again and again, so that several copies of the audio are playing at once, but not in sync. Then the 'Start Calibration' button is greyed out, and I cannot start calibration at all. I've tried on my laptop, and I can start calibration, but the Chinese audio plays there as well.
Finally got a solid calibration of VPS, and took the P4 back outside. Same message. I do notice that the message goes away when I rise above treetop level. That prompted a proximity test. I can get within 30 - 40 feet of an obstacle (in my case, trees) and the message appears. Obstacle avoidance still occurs normally at less than that distance.