Mate, I dont think it got all that extreme. But, when I last took it off and tightened it back down, temperatures here were in the minuses for a couple of months. With the onset of spring, we have been having 20+ days.
Corrector plates are most commonly removed to gain acess to the mirror for cleaning. Anyone who's scope is out of warranty may have done this, as I have. It never even occurred to me to consider metal and glass contraction for the chance of seasons.
My windscreen on my car did the same thing to me a few years ago. A cold morning, turned on the demister and watched a crack go from one side of the car to the other in about 15 seconds....
It doesn't help that correctors are PAIRED with the primary mirror on manufacture. You cant just order a new one in the mail and chuck it in.
Now I know. Doesn't help me, but perhaps this warning can save others.