Unless this is a known issue and others chime in with advice (I've never heard of it myself), my first thought would be to call HK CS and tell them exactly what you posted. I'm sure they'll be interested to hear it. Contrary to what used to be popular opinion, HS CS is top notch nowadays. They'll take care of you.
ETA: Question - is the pistol hard to rack with any ammo now, or just the Lehigh? In other words, is the pistol inherently acting different now?