Wow. If this was as common for others as it is for you it would be much more written about it on the Internet.

I`d say vibrations, becouse the piece that broke is not carrying any vertical weight. I never liked the truss thingys becouse it sticks out so much. Instincts tell me to keep weight close to what is carrying the weight and not on parts sticking out like that.

This is why I wanted a Brompton truss on my Curve. First I carved out exess plastic from a B carrier block. This made it weaker so I filled out the empty spaces in there with hot glue. Kept thinking "hmm, is it strong enough?" Then I ordered that adaptor thingy that has been presented here. I have not installed it yet. This problem is tumbeling around in my head like in a tumble dryer: Is my carved out carrier block hack stronger than using a regular carrier block with an adaptor? Last question becouse with the adaptor you only rely on the screws plus it puts the carryer block (and therefor the weight) further away from the frame than it is intended to be. Also both on the B carryer block and the truss thingy there is a carved out area that goes over and around the welded on metal thingy and I am sure that gives some extra support that you do not get when it is sticking out like with the adaptor.

Several years ago when this problem started bothering me I bought a "truss" that was much shorter, keeping the load much closer to the frame but this can only be used on small bags. Bromton bags (trough the frame) is atatched at the bottom of the bag. Therefor you do not need a long truss thingy. Clickfix bags/baskets are atatched at the middle or top so you need that long thingy to keep the bag away from the frame and wheel.

Frame bracket (for handlebaradapter on head tube threads) (0211R)

Rixen & Kaul, KLICKfix Adaptersysteme Fahrradzubehör, Solingen, Taschen, Körbe, Werkzeug

I only use the Caddy becouse it keeps the weight close to the bike so less vibration and damage from weight hanging far from the bike. I recently bought two "truss thingys" for seatposts, one for my B and one for my Curve. I only intend to use them on holydays and with a rack supporting the weight under.

You should contact Clickfix. They should be interested in this. I do not expect much reaction from Tern.