The 78s don’t have good volume so can’t take larger sized pallets, and the problems with the rollers are the Rolls Royce (Trent) materials issues and also something to do with the bleed air system (or lack of) adds up to an engine that’s highly stressed and every issue they solve puts another part of the engine under stress. Also there’s an issue with resonance at some power settings. There’s a bunch in our company with EDTO limitations. The engine is fairly similar on the A350 and they’ve had the odd one go boof too.