Soft shadows is what is doing it . I no longer use them. I find it is easier and quicker to use mor elights in tightly grouped arrays than it is to use soft shadows.  I use light domes and light groups to get soft shadows.Soft shadows in Bryce are amazingly slow. I fidn that 3 soft shadow lights are slower than 100 hard shadow no falloff lights. Remember too no falloff.
    Sort of as an experement I rendered a pic with 60 lights and another with 3 soft lights the 60 is substantially faster. People don't play with light domes because they are slower but because they simulate soft shadows and true ambeince faster than setting up a render for those things. My 3 sot light s is still at it at least twice as long as the 57 light rig. I have preset ligting rigs for this I made my own after I took a few of the ones available and disected them.

The wit of a misplaced ex-patriot.
I cheated on my metaphysics exam by looking into the soul of the person next to me.