Do you know why the poly had that issue but the nitro didn't?
Think of it this way (this is my theory, it ain't proven fact):
Styrene boxes are much harder (and more brittle) than Saran Wrap. Yet both are plastics (nitro is a type of plastic).
Saran Wrap is a plastic that clings to what's inside it, regardless of temperature and humidity changes, but the Styrene plastic box isn't going to conform its shape to the food that's in it if the temperature and humidity changes.
This is due to differences in the chemistry of the materials.
Poly is a hard plastic that creates a thicker finish, more like a shell. It dries pretty stiff; it also doesn't adhere as well as nitro. It's more like the Styrene box.
Nitro is more like the Saran Wrap.
If the guitar is bumped, or the wood inside the hard poly "shell" shrinks for reasons like temperature and humidity, the wood moves and the paint doesn't always move with it. It separates, and can get cloudy.
Like the Saran Wrap, Nitro stays comparatively malleable and sticks to the wood better. So it doesn't separate as easily. That might also explain why nitro guitars sound a little different than poly guitars (this may be controversial, but it's based on experience with lots of guitars over a period of 58 years - it's an opinion I've formed and I can't objectively prove it, so YMMV).
Granted, like any material, each finish has its pros and cons, and in this case the nitro is more delicate. But the primary function of the guitar is to be a wooden musical instrument. The nitro compliments that function pretty well; in fact, its greater delicacy works with the instrument in its primary function, instead of against it.
As a result, it's my belief - opinion - that nitro is a more complimentary finish for a wooden instrument than a harder poly because it 'follows the wood' a little better, whether that's referring to the wood's hygroscopic nature (swelling or shrinking due to humidity and temp changes), or referring to the fact that the wood is allowed to vibrate a bit more freely.