Composite and UPVC door locks can be affected by a sudden drop in outside temperature. The door frame will start to contract, which can result in a poor fit between the lock and the door frame itself. You can start to have problems lifting the handle to lock the door and might be tempted to force the handle and damage the locks.
If this starts to happen, it’s a good idea to call your local locksmith to service the lock and adjust the striker plates and hinges. Don’t leave it to fail as you might find yourself locked in or out of your house.