I'm having trouble applying a bevel to curve I am fairly new to Blender, and I'm having trouble with applying an object-bevel to a Bezier curve.  I've had success in the past, extruding one object around the contour of another, and I have even tested applying the bevel to a simpler object in my current .blend file, and it works, but when I try to extrude the circle object around the curve of the saddle-shaped object, the saddle-shaped object just disappears in a weird way.
Here is a shot of the three objects in my setup: on the left is the saddle-like curve I'd like to give a thickened, circular cross-section, and I want to use the small circle in the middle to do it.  The square on the right is just there for debugging.

In this next photo, I've successfully performed the bevel operation on the square to the right -- you can see it took the bevel operation, and now has a diameter of 8mm.

However, when I try to apply the same circular bevel to the saddle-shape, the saddle-shape just disappears, though I can see weird, flickery traces of the old shape:

I've made sure the scales of the objects are compatible, and haven't come up with anything in searches.  I'd really appreciate anyone's help with this!
Thanks in advance.
Nevermind, I've figured it out: I just had some vertices which were too close together.  I'd already tried merging by distance at 1.0 mm, but it required a merge radius of 2.1 mm before it would finally take that bevel.
Cheers.