Verified answer

I assume you have inspected the clock for ant damage that may have occurred between the shop and your home. I further assume there is no indication that the clock was dropped, crushed, banged or otherwise hurt. Based on that I offer the following suggestions:

It sounds like you have one of three things going on.

First: Did a piece of packing get into the slot where the pendulum attaches. I have seen where nothing more than a piece of shredded newspaper can cause enough drag to cause a problem. Take a good flashlight and a small mirror and have a real good look for anything foreign in that area of the clock. If you can open the back to expose the motor, do so, and look for anything that doesn't belong there. Be careful and not bend anything while you are poking around. If in doubt have a clock repairman have a look at it.

Second: It may be wound too tight. One weight powers the cuckoo and the other drives the clock motor. If one of the weights is jammed against the bottom of the clock there may not be enough slack in the chain to raise the weight that tiny fraction needed to allow the cogs in the clock to unlatch and let the weight down one link. If this is your problem I suggest a clock repairman as your first option. Manually releasing this requires knowledge of the clock motor and some experience with cheating it.

Third and the one I see the most: Pendulum clocks HAVE to be ABSOLUTELY level or the pendulum doesn't swing far enough in one direction to unlatch. Use a 6" torpedo level to check that the clock bottom is perfectly level. If you can't do this or don't have the tools, you probably have a neighbor who can. Ask the neighborhood tinkerer (is that a word?)to help you.

Good luck and Merry Christmas

Some cuckoo clocks I've seen have two different sized weights. Check to see if the heavier weight is on the pendulum chain.

The chain could be pulled up too tight.