Hi guys my ER9 RD (s/n 250123x) also died after going through a very short patch of uneven pavement at ~ 25 mph a week ago. The same problem that it makes sound but is stuck at the smallest cog. I contacted both 80 designers store (the seller) and ltwoo. Heard nothing from ltwoo and 80 designers is dragging their feet with responding. Only one reply from 3 days ago so far and it was for asking me for a video. They've been ignoring me since.

I was just about to order one more set for another build and this happened. Maybe I should just bite the bullet and get the 105 DI2.

I'm here to report back on the issue. I never heard back directly from Ltwoo sadly. On the other hand 80 designers on Ali, albeit incredibly slow, finally sent out the replacement RD today (6/25) after 3 weeks of back and forth and two separate videos showing the RD is indeed broken. On top of that I have to pay for shipping (USD $15+tax, which should not be taxed by law but anyway).

I have to say I enjoyed the group set, when it was working. Maybe the downshifting in the rear isn't as crispy but it still worked very well (and maybe because I have a 11-34 there). And the weight and price point are incredible comparing to 105 di2. However this whole ordeal left a very sour taste. First of all, how on earth would the RD break itself simply by going through an uneven patch of pavement less than 10-12 ft long? There's something very wrong about the engineering/material here. And then there is the customer service, or lack thereof. Ltwoo never directly responded to my email. And I really don't understand why it took them a whole 20 days since they first received the video to agree and send out a replacement. Ltwoo should be ashamed of themselves for doing business this way.

i really was going to order another set for my other bike's upgrade right before this happened. But I'm holding out now until I see how Wheeltop/Magene handle their QA/QC and customer service, though to be honest I don't have high hope there either. Or maybe this is the universe telling me to stop effing around and just stick to the mechanical 105 for now.