The Champion was Vibroplex's "low-end" bug, and the other models do work a bit more reliably. (I realized this even when I purchased my first Champion brand-new for $29, I think, in 1966. I didn't have the money for a Blue Racer or one of the better models.)
Remember, the bug is a purely mechanical device, kind of like an old-fashioned (crank-type) egg beater, manual pencil sharpener, etc -- it's up to you, the user, to do everything exactly right in order for it to make dits. If sometimes the lever doesn't bounce, there are a few things that can cause this. Make sure that you have the spacing between the lever arm and its "dit" stop post set correctly for the amount of pressure you normally apply when sending, and also for the speed range you operate.
What starts the lever vibrating is the motion of your thumb against the lever paddle, which moves a short distance then suddenly stops when it hits the mechanical stop post. That begins a sypathetic vibration of the lever, which is continued at a certain frequency based on the weight position on the lever (near its end) and the spring of the "dit" contact U-spring which bounces against the "dit" contact.
The weight position, lateral movement distance and U-spring "dit" contact spacing, all of which are independently adjustable, determine how well the "dits" will really work, at at what speed. Every time the weight position is moved, the other two adjustments should be re-assessed to see if they are still proper.
Still another adjustment is the spring tension of the lever paddle. For a heavy hand, you'd want more tension; for a lighter touch, you'd want less. And every time that adjustment is made, which is still another idependent (thumb-screw) adjustment, the other three need to be re-assessed. If you make the spring tension of the lever paddle too heavy, and then use a light hand, the lever arm will never begin to vibrate, and you'll send a "dah" instead of a string of "dits."
There's no question that this all takes some practice. I think it took me six months to be able to routinely adjust my bug (without having to think about it), and that was six months of daily use, back in the mid-1960s. Then, of course, I discovered the electronic keyer, and never used a bug again!