Wait a second!!!! With a 24mm lens, and a longish extension tube, the
focus point is VERY likely to be ___inside the lens itself____.
When you use a short focal length lens with an extension tube, it needs to be an incredibly short tube: Nikon made some VERY short tubes, in the 1mm to 5mm length, for use with wide-angles. Most all normal-length extension tubes will NOT allow you to do close-up shots with a 24mm lens. That is just the way it works.
(The Nikon set of VERY short tubes has K1,K2,K3,K4,and K5 tubes in the complete 5-tube set.
**EXCELLENT** Nikon K Series Extension Tubes, Set of 5 - K1, K2, K3, K4, K5 • $39.07) and pre-dates digital photography by decades. THIS is the type of extension ring needed to allow close-up shooting with short focal length lenses. As you can imagine, these extension tubes are very short; so short they do not look like "tubes" as much as "shims".
NIKON-K1-K2-K3-K4-K5-Ring-set-_1.jpg
Try it for yourself and see. If you have a 24-70mm zoom, mount the tube....it's VERY likely that you will find it impossible to focus at 24 to 35mm with a longer tube, like say an 11mm tube, because the focusing range will be, literally, INSIDE THE LENS (a dentro!). However, at the longer focal lengths, from 50 to 70mm, the tube will allow you to shoot close-up subjects.
It's very likely that there is nothing wrong with the tube whatsoever, but you are using it with an incompatible lens.