It doesn't seem like a mechanical issue. Whenever I try to upshift, it just flashes a red light. The FD shifts fine. I tried several hard resets, swapped batteries and switched the plugs around. My other ER9 bike is running like a champ. Thankfully I have several bikes in case one goes down!
hihihi, welcome to the club. I wish i had good news.
My 3 dead RDs would make a weird noise and refuse to upshift, and i was never offered solutions. I managed to get 2 warranty replaced, and not the 3rd one, at which point i gave up and made plans to buy them new. One of my friends bought a spare RD for 150 eur on AliX as insurance policy, so he can keep riding if his RD dies. His and mine are the only that havent died from the batch of 5 we ordered last year.
I'm still riding with mine, i've put almost 9k km on it. The charging port is half broken because it's a bad design (worst case i charge the batteries in a dedicated lithium charger which i already have), but other than that, the group works super well, so assuming i can source groups at a good price (c.400 usd for shifters & FD/RD + brakes), then what i plan to do is order than AND a spare RD, because in the west, 150 EUR is basically a visit to the bike shop, so it's a good insurance policy.
That logic quickly breaks down if the price of the group goes up.