Here’s a long discussion by Lennard Zinn on bike geometry issues related to wobble and mechanical resonance.

https://www.velonews.com/gear/techni...speed-wobbles/

Worth noting here, per our previous discussion, that a number of his customers came to him with serious wobble and resonance issues on stock carbon frames. Point here is that it can happen to anyone given the right conditions in bike construction, geometry and adjustment when presented with that variance in order weight, body position, and riding conditions.

Mechanical resonance issues are tricky and very often counter intuitive to solve.