The gears work fine across the whole cassette on the inner ring but all of a sudden the chain has stopped engaging with the upper jockey wheel when in the big ring and three largest (easiest) sprockets of the rear derailleur.
The jockey pulley looks out of position when this happens (almost horizontal to the lower tension pulley jockey wheel - the chain then simply isn't reaching the upper jockey wheel) and the chain makes an unholy racket with the drive train eventually seizing up entirely until I shift into smaller (harder) sprockets.
This seemed to occur straight after I removed then replaced the rear wheel, catching it a little on the brake pads as I did, which resulted in a bit of a clunky removal.
Is this likely to be the result of a bent, misaligned rear derailleur?