Not to make light of an aggravating situation, but there is a packaged explanation for this.
Back in the fifties or sixties, one of the spooky TV shows, maybe Outer Limits but more likely Twilight Zone, had an installment about the Time People. The premise was that the only reality is what you can see. Stuff in the other room doesn't exist until you go to that room. Between the time you decide to go to that other room and the time you arrive there, the time people are frantically creating that other room, laying carpet, moving furniture, hanging pictures the way you think you remember them, that kind of stuff. Sometimes the time people get it wrong and miss a detail, like the keys you think you left on the table, but which aren't there when you look.
So, it's in no way your fault. Under the bench does not exist while you are working, only when you look there. And if the time people neglect to put that thimble, errant fly, or #52 drill, where you can see them, it' not your fault. Go have a beer while they get there act together.