Not really an ER9/X issue, but the other day when doing a climb segment, I heard a loud pop and realized 3 of 4 rivets on my front derailleur hanger had popped off. It happened when I was shifting from the big to small chainring. It's the same issue that occurred with Trace Velo's Trifox X18 frameset. My TFSA frameset is using the same FD hanger with 4 rivets. My guess is that the extra weight/torque of the ER9 FD + chain catcher I'm using eventually wore out the rivets. Luckily I was able to ride back home. So I cleaned up the frame, added an adhesive back to the hanger and re-riveted it back in place. The new rivets are stainless steel and I opted not to epoxy the hanger onto the frame. From a few YT videos I saw, even epoxied FD hangers can break, tearing off part of the carbon.
Anyways, it's probably something to keep an eye on, especially if you're using an older frameset.