Not sure if someone suggest this or not. Possibly the short USB cable was pinched, and you left it plugged in when trying the other cable. Only one USB should be plugged in at a time. Unplug the micro USB connector on the upper left corner to activate the other larger USB port. Otherwise it won't connect.
Try to downgrade with dji assistant manually. One by one. Download the assistant to your pc, connect the bird, turn it on. Open dji assistant, chose ur bird or controller, whatever is connected and go to firmware. There choose the .400 and do the downgrade. Same with controller. It should work...
This is happening to me as well not a new pilot new S8 can't get it to reliably connect to the phone coming from a Samsung Note 5 with no problems just can't get it to work for my S8
Update 2 I've received the Drone back,DJI paid for all the postage and replaced the controller.only glitch,they sent back the wrong phone cable and forgot my memory card.Ive emailed them and I'm sure they can pop it back in the post.Happy with the customer service.