Well, somewhat mysteriously my Mini and RC now communicate once again, and I thought I'd explain what I did .. even though (to me) it makes absolutely no sense.
I was unable for several days to get the AC and RC to pair. I was online with DJI support and their conclusion was ... send it in. The final straw was when I plugged the drone in to my computer and try to use DJI Assistant 2 and I always got the error message "USB device not recognized ..."
The morning before boxing it up, I thought I'd try one last time. Now, I had removed the SD card to copy some stuff off it and forgot to put it back in the Mini. I powered up the drone and then pressed the power button for 4 seconds to put it in pairing mode, then turned on the controller (without my phone connected or the DJI fly app running). Within about 3 seconds, I noticed that the bank of four lights on the controller had stopped flashing and were solidly lit (side note, I WAY prefer the Spark green light/red light system to indicate connected). I quickly plugged in my phone, booted up the app and voila! the phone screen showed what the drone camera was pointed at. I next grabbed the SD card, plugged it in and immediately the AC/RC connection was lost. Hmm, I figured I must have done something inadvertent so I repeated exactly the same sequence ... got the AC and RC connected, plugged in the card and pffft, connection lost.
So, I reformatted the card, tried again and everything since has been just as it should be,
the only piece of evidence that tells me it might conceivably have been the card that was at fault was the error message from the computer that the USB device wasn't recognized, assuming it was trying to read the card (which was still always readable directly by the computer outside of being inserted in the drone). This particular card was in the drone when I did the firmware update .. and I should note that I commonly removed this card to copy other files to it that were drone-video related, etc.
So ... now I have a workable drone but a lingering sense of doubt that a SD card could somehow prevent the AC and RC pairing.
cheers
Steven
(ps - I'll post this over at DJI forum as well just in case anyone else has a firmware update-related issue)