There's no real way to solve this and still stay within the NI ecosystem. Absynth also suffers from the same bug. What makes it hard to squash is it's intermittent even within the same session. One thing that will definitely cause hanging notes is unresolved MIDI sustain messages. Stop play before getting a sustain off message and you'll get hung notes for sure.
Now I don't know if Kontakt 6 or Reaktor 6 fixed these issues and Absynth hasn't had an update in a dog's age.
Don't even bother asking tech support at NI - they're supremely incompetent. I asked a question about support in AudioSuite in PT and they didn't even know what that was
The NI forums aren't much better either.
There's one reason I haven't gone full-on EW Play with everything - EW's libraries are very pricey and the early stuff has crappy sampling. But I've not had any problems with Play 6 engine/libraries. I'm actually looking at UVI Falcon for sampling duty.