Maybe a variation on what you're experiencing, but I have a bike with a shock-absorbing stem that amplifies a paving irregularity as I descend a nearby bike-pedestrian bridge. First time I experienced this it nearly had me crashing into the bollard at the end of the ramp. Very sketchy.
I feel the undulation on other bikes but they don't amplify it. Learned to use back brake only when slowing my descent and that lets the stem travel but not transmit as much vibration to the entire bike. The whole thing is very weird, and site-specific.
Have experienced oddities on long descents with other bikes and just had to cope in real time, usually getting off the saddle and moving my weight back. Sometimes, rural roads will have periodic irregularities that a road bike will resonate to. Exhausting to ride. IDK how folks race cobbles.
Motorcycles with bad suspensions and whippy frames are a whole other level of "fun." Some were even given a shock to stabilize the steering, which to me was always a sign to "stay away."