if you are smoothing, press shift, click on where you want to smooth and hold, then let go of shift and continue smoothing. Releasing shift activates a different smoothing algorithm that is better for this kind of topology.
Sorry for this 2 year old bump, but I just came across this post, after another desperate search how to solve this issue with spikes popping op when smoothing a dynamesh shape, and the release shift smooth works like a charm! So thanks!!