I get the same with most any turbo-prop float/amphib. Don't know if this is a real-world problem.
I reduce the 'fuel conditioner' to low idle.
If that isn't enough then I tap the F2 key a couple of times reduce the prop thrust. Again, I don't know if this would be done in the real-world, but it works for me..

Dave
At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation.