Bowed rotor is a common problem, affecting most new technology turbine engines. It's exactly what it the name describes - differential cooling of the HP rotor causes it to bend or bow. As a result, there is period after shutdown - anywhere from a few minutes to several hours after shutdown depending on the engine - where restarting the engine will result in issues - anything from high vibrations to blade rubs and -worst case - blade damage. To achieve max efficiency, designers are minimizing blade to case clearances - good for efficiency, but makes bowed rotor start worse.
I have no first hand knowledge of the NEO issue, but I'd bet pretty good money that it affects all the PW geared fan engines to a similar extent.
To be fair, it also affects the Trent, GE90, GEnx-1B and -2B, LEAP, and to a lesser extent, the CF6...
Last edited by tdracer; 6th June 2016 at 12:17.
Reason: fixed typo