They look good on the outside but are dried out on the inside.
If you were here, the answer would be drought. It could really be any number of things, though. Lack of water, lack of nutrients in the soil, disease.
Could be that the growing season this year was too short for whatever cultivar you have. Pecan development in Oklahoma was about two weeks late this year. So if you have a cultivar that ripens late, this is what can happen.
Likely one or a combination of two things:
As devon mentioned, the growing season was delayed by two weeks. This influenced pecans in two ways that could have caused those low-quality kernels.
First, most kernels were in the "filling" stage somewhere between Sept 1 and Oct 20 this year instead of the normal Aug 15 to Oct 10. If there was no moisture available during some of this period, the kernels could end up looking like that. For this year our moisture here ended Aug 10 or so and there was zero more until the end of Sept so the trees that are late maturing had no moisture available (unless the soil was very deep and good) for a few weeks in late September. This still is not always a big problem unless the tree has a large crop to fill or if the soil doesn't hold much moisture.
Secondly, the late maturing nuts (like some of the more southern papershells like Choctaw, Stuart, Maramec, etc.) ran out of warm days and sunshine to complete the filling process before the trees started going dormant. My Maramec trees looked like those kernels for this reason. I would have thought that since we did not have a freeze until November that even my late cultivars would still be able to fill out but the ones that had large crops and needed long growing seasons still didn't complete the process.
This is still just an overall guide though and there are some other things that have a small chance of having contributed. Sometimes trees that do NOT have big crops or that do NOT have large nuts can still fill out the kernels well even when the weather is dry or the season is delayed. The bigger the nuts and bigger the crop and the longer season needed by a specific cultivar or native tree all causes more risk of the nuts being poor in quality like those.
Like I said, my Maramecs and a couple others that had large crops or not very deep soil looked exactly like that.
My nephew in southern Oklahoma who normally sells thousands of pounds didn't even get his equipment out of the barn this year. He said the crop just wasn't worth the effort.
I have harvested half my crop.
Unfortunately there is a lot of cleanup required before I can get going again thanks to the ice storm.
The tree should have had water. I keep the bed it was in watered and feed with 13-13-13. Does this make a difference?
How large is the tree and how large was the crop on it?
Was there anything else unusual about the nuts? Were the shucks on tight on many of them when you found them? Did the same tree produce nuts that varied a lot in size and somewhat in shape?
Some of them were were odd shaped. it took them forever to fall from the tree. The tree is large. probably at least 50 years old.
Do you have an estimate of how many pecans were on the tree? A tree that size is capable of a 200lb crop under good conditions, but 100 lbs would be a decent crop. A 5 gallon bucket of nuts could weigh from 20 to 25 lbs.
A tree that size with a large crop would need a few thousand gallons of water throughout the rooting area available during the filling process to satisfy the tree and nut requirements.
The odd-shape ones are often due to pecan scab disease, but this usually makes the nuts smaller than normal and yours look good sized. Other diseases in late summer also could cause poor quality due t shuck problems or early defoliation combined with a big crop and late maturity.