The cup came loose and with no way to tighten it on the road it kept loosening and jamming the cranks. I eventually gave up, cycled through it, crunch, crunch and the plastic was mangled, but I could finish my ride to work then home in the evening.
As I’ve done before, my Nexus bike donated the parts to fix bluebell, its bottom bracket is UN54 too. Different models often have slightly different cups, so I am fortunate they are the same model.
I’ve ordered a UN55 for the replacement, that has alloy cups on both sides, I’m unsure if that’s wise, but only time will tell if I ever get it happen again.