I've had two such tank slapper incidents. The first was on a Gen1 Vmax at 'high' speed. It was so violent and extreme wobble that after I escaped from that without incident, I sold the bike. This was in '91, going thru the hills of San Clemente while following some new generation sport bikes.
Years later a second incident was a bit of a revelation. It was on a 1200 Z-Rex and I was just doing what I thought was a normal 'spirited' acceleration, but I had my weight shifted more toward the rear and I was a bit more upright with arms outstretched further than I normally ride & I found that just this amount of unloading of the front fork was enough to initiate a strong wobble. I backed-off enough to get more of my weight toward the front and it immediately stopped. From then on, whenever the front started feeling too light, I just bend the torso forward and it's enough to stop any wobble. This seems to work on any bike I'm on.