So looks as though the ferrules are on correctly, but maybe you didn't tighten the nut up enough? You're meant to go 1.25 turns or so. Which of the ferrules bound onto the tube, as there should be no gap between them? Looks like a very big gap between the sealing ferrule and the end of the tube too...
Oh - it got tightened up enough alright... After it leaked the first time I was giving it another 1/2 turn until it didn't tighten up any more.
Either the tube wasn't quite round after my bodgy tube bending efforts, or the ferrules were too big for the tube (cheap aliexpress compression fittings).
Usually I go for occam's razor... which doesn't seem to narrow it down for me.
EDIT: D'oh pic was demo only on a spare piece of tube. It most certainly wasn't tightened. Ever.
