My latest singing bowl arrived a few weeks ago and first it didn't sing well with the others. Then It sang nice with one in particular. That second bowl 'became friends' also sings nicely with a third bowl. But the third bowl isn't singing well with the one which just arrived. I hope that make sense. The weird thing is sometimes they sound good together sometimes they don't. And depending on which of the two bowls I play the second one with (the one 'getting along' with the other two, which don't get along with each other), the bowls seem to emanate different combo tones. I heard that old metal singing bowls produced multilayered tones. So that one bowl has several different tones. It is almost as if the bowls have to be 'seasoned' to play together. As if it grows with time to tune in with its friends. I am sure there is a scientific explanation for this phenomena. But I found that to be quite interesting!
You might be playing the bowl in a particular way that gets one tone out of it - and as you go along the 2nd tone takes over. There are ways to strike or "scrape" the clanger along the edge of the bowl to get it to emit more of the high pitched sound, or more of the base sound - you have to play around with it.
Or... clang the bowl, and then immediately place the clanger on it's edge and swirl the clanger around the circumference, whist it's still vibrating.
There's also "entrainment" - when one vibration draws another into it - or makes something else vibrate along with it. Thus the opera singer is supposed to be able to strike a note that can shatter glass (the glass molecules "entrain" to the sound vibration and then vibrate at a frequency themselves that means they can no longer be stable).