Well I've been using it for ages without any problems, to my mind it's way better than Pledge as a gloss varnish (Klear isn't sold anymore).
As to why it happened, there's a myriad of possible reasons - bad batch, humidity, moisture in the airline (if sprayed on), temperature... frankly it's impossible to give a definitive answer. It's just as likely that the problem occurred during the application, especially if it was airbrushed on. Crazing is often the case if the
airbrush was too far away from the model.
As to fixing the damage, a second application might work - that's easier than stripping it back & if it doesn't work, you've not created any more effort for yourself.
If it's an aircraft, I'd say try rubbing it down & reapplying the gloss coat. If it's armour, apply another coat & hope it works to cover the cracking.
Fingers crossed Alan!