I changed a Bb Clarinet to A Clarinet, and it played back far too loudly. I changed it back and have the same issue. I checked the mixer to ensure it was at the right levels.
The instrument does not seem to respond to dynamics correctly now. I am using NPPE.
Is this a known issue?
try re-applying the playback template
If you mean selecting another playback template (like Halion) and then selecting NotePerfomer again, that did not work.
I fixed this by adding a clarinet in A, copying all the Bb clarinet parts to it, and then deleting the Bb clarinet.
CORRECTION: That DID NOT fix it.
Sorry for your trouble with this. 
It’s possible that in the copy (and subsequent paste) that everything was not truly selected. (You would have been better served to change instrument in Setting mode but that’s water under the bridge now.)
Can you post a file? Someone may have an easier answer to fix this. (Or, if you can restore from a backup, you can try a different approach or better “grab” for the copy.)
An old adage is from the old barnstormer days: “Never leave hold of what you’ve got till you have hold of what you want!” In other words, don’t delete the original until you’re sure the new one works! (And save your files with revision numbers, or date & time!) 
— Jim
I meant Play->Playback Template …->Apply and Close
But I think that wouldn’t have worked if switching to and from another Playback Template didn’t work for you
Which playback engine are you using in NP?
(Just speculating there might be an issue with the underlying library?)
With standard NP5 I cannot replicate this problem when swapping between clarinets.
I will check and reply. Thank you.
Thank you very much. I save versions in several places, so no issue going back.
I have checked and the problem persists whether I use VSL or BBCSO, and whether I change the instrument or add an A clarinet and move the part to it.
WORKAROUND: I created the audio file using the Bb clarinet, but created a set of parts and score with the A clarinet.