A possum or skunk would leave evidence. A raccoon might carry them a short distance away from the nest to a safer spot but won’t go real far with them, unless it has babies in a nest not too far away.
A snake will take a few eggs, how many depending on its size, and leave no evidence, but it usually does not come every day. The digest the eggs before they come back for more. That might be a couple of days or several days. If it is every day it does not sound like a snake. Besides snakes won’t dig under a fence. It will go through existing holes somewhere. How cold is it where you are? Are snakes even active?
A canine will take eggs and leave no trace. They will also dig under a fence. You would expect a fox or coyote to have more interest in the chickens themselves though instead of the eggs. A dog might be more interested in the eggs than the chickens. You really can’t tell for sure what a predator will actually do. They don’t always read the book. With that digging under the fence it sounds like it is probably not your pet dog.
A human will also take eggs and leave no evidence though they generally don’t dig holes under a fence.
Chickens that eat the eggs can sometimes eat the shell too, but in my experience they don’t always. And you should see a soggy mess in the nest if it is chickens eating the eggs.
Having holes (plural) dug under the fence doesn’t sound like a predator either. You’d think they’d reuse one if they dug it. Are you sure it’s not rabbits or maybe a groundhog doing the digging? Have you seen tracks where they go in or out?
I’m not convinced it is a predator, mainly because it is so consistent. Normally predators don’t show up and wait for practically all eggs to be laid but take what is available. Some days you might get several eggs, other days none or not much.
Are they hiding a nest? That’s one of the top reasons for lack of production when they are actually laying. If you can, try locking them up all day in the coop or coop and run to see if production increases. That may mean you locked out a predator instead of keeping them from going to a hidden nest but at least you will know they are laying.
A second thought is that they have simply not recovered from the molt. Some chickens finish molting in less than two months, some may take as much as five months. It’s not about how fast the feathers grow back it’s about how fast the feathers fall out. A fast molter will drop bunches of feathers at the same time and look really awful. A low molter may never look like they are molting, you just see a lot of feathers laying around.
From them molting in October I’ll assume you are north of the equator. It’s still winter here. Some chickens will start laying as soon as they are over the molt and have built their body reserves back up to the level required to lay, but many will wait until the longer days of spring before they start. You could be experiencing that.
It’s hard to say from here why you are not getting eggs. From the time of year my guess is either they are not over the molt or they are waiting for spring. A hidden nest is possible but probably not likely. While the holes under the fence are troubling, I don’t think it is a predator, but anything is possible.
