Well I'll be dipped. As a last ditch idea to relink my PS3 with Litchi and DJI Go, I went indoors and switched off my Wifi transmitter. Lo and behold, the drone connected with both Litch and DJI Go instantly. Relieved to see the link restored, I went to start the motors, but then got that "IMU calibration", which for me generally means it is time to pack up and try flying another day, since IMU calibration NEVER ends, in my experience.
I suspect that the IMU calibration error is somehow related to Litchi, since it rarely ever appears when I use DJI Go. Once the IMU calibration message does appear, however, it blocks all motor start attempts in BOTH Litchi and DJI Go, for hours, such that I now just quickly power everything down the instant I see that IMU message, and call it a day.
Matter of fact, it is because of the IMU calibration error message, that I stopped using Litchi altogether for a while, and only decided to try Litchi again today, because I finally figured out how to download Litchi flight plans from my desktop to my iPad. Haven't given up entirely just yet, but if I continue to see the drone grounded by the IMU message every time I try to use Litchi, I will most likely stop trying to use Litchi for good, and stay with DJI Go, much as I would have liked to fly saved missions with this drone. Some things just aren't meant to be ha ha.