The recent avionics certification standards (DO-160 in various versions) all specify a ground survival temperature of -55C. Your equipment will have been tested to that level, but will not necessarily have been subjected to multiple cycles that cold. At very low storage temperatures (usually below 40C) the fluid in LCD screens will partially freeze, just like water. It will thaw out again, and work normally, so there is no irreversible change in the fluid.
The problem is that when it freezes it makes crystals, again just like water. If you are unlucky, these crystals can damage the inside coating on the liquid crystal display, which manifests itself as "stuck" pixels on the screen when the display is back to working temperature again (usually stuck ON). These broken pixels are only a cosmetic defect until eventually after many freeze/thaw cycles they will become sufficiently irritating that you will want to replace the screen.
(I haven't had to replace an EFIS screen, but learned all this when working on a consumer electronics LCD screen product in a different life).