I think I need a a diagram to understand how a loose chain could cause the sprocket to flip off. What happened to the bit of metal wire we saw in the early photos? I could just about imagine a freak accident where the wire got tangles between sprocket and frame and dislodged the circlip. Anyway, great to know Thorn are helping to keep you on the road and I hope the rest of the tour goes smoothly!
The spider on my Schlumpf HSD is held in place by a circlip and I run twin chainrings.
If I get the change between ring wrong under load, when the chain is quarter shifted there is enough twisting force on the chainrings to pop the circlip.
It was mainly on the upshift but I have popped it on the downshift as well.
I've now learnt to treat the shift more like hub gear shift and have gone well over a year without this happening.
The main difference is the HSD has a round circlip in a round groove while the Rohloff has a square clip in a slot, so the Rohloff will need a lot more force to pop it.
But if something does jam in the chain and it starts to unship under load, if you're very unlucky and everything lines up right, then I can see the sprocket getting forced off.
