Retraction is set to 40mm/s, I presume that's the default as I cant remember changing it.
I think I may have a better idea now. It stopped feeding again but as I was pulling out the jammed filament the bowden tube popped out too, a plug had formed at the end. The alu and bottom plates are at a bit of an angle, with the nozzle side being lower than the fan side. I think the bowden tube and white connector are not meeting flush, although I thought with the new hot end design the molten plastic wasn't supposed to get that far up.
Could it be that the long retractions are pulling moltem material further up the tubes than you'd otherwise get?
I'll take the whole carridge apart and see if I can get it aligned a bit better, maybe try a spacer on the fan side threaded rods to keep the middle and bottom plates a bit more squared up.