I dunno? I've never had walnut trees. Start hitting the search engines!

Sorry, I thought you had discussed walnut trees at one point. Thanks!

No prob!

Maybe they were stolen by squirrels? Also, we had some weird temps last winter and this summer. It is possible the right pollinators (if walnuts happen from pollinators) weren't active when your tree was ready. Was there another walnut tree nearby that got cut? Some trees will have fruits only when a second specimen is close enough.

But here is the most probable cause, from here:Walnut tree not producing nuts: Causes and how to fi...

Walnut trees are biennial bearing, much like mangos, apricots and avocado. This means that if they have used their available energy and nutrients to make nuts one year, they focus on flower production the next year. There won’t necessarily be no walnuts harvested during the blossoming years, but there will be fewer.

Thanks! I suspected it might be something like that. The squirrels couldn't have stolen them, because they were pretty darn obvious the other time.