If the pictures are of what you call a "stick on black rubber disc"...it is really a liquid filled, variable deadrisd, shoot thru the hull ducer.
I have one and it works great. Certainly not cheaper tech, just a shoot thru type that you no longer have to build your own tube for.
About every ducer I have ever used seems to lose a good signal from something. Either speed, tubidity, thermocline, etc....
Sometimes adjusting controls overcomes one, but then the settings are wrong if you encounter another.
Usually speed will kill a transducer if any irregularity on the bottom causes a bubble stream across the face. Weed growth, barnacles, rough paint, thru hulls, etc all are potential causes.
Occasionally I hear about transducers that should not have problems, all causes have been investigated yet they lose their signal. I am perplexed by this as much as anyone. Even the equipment manufacturers seem to run out of suggestions other than move the ducer around...great for shoot thrus, not so easy for thru hull ones or transom models. Then the suggestion is simetimes, get another ducer and move it around in the same conditions the other loses bottom. Again, not so easy unless you are a marine electronics store.