<< you can fillet the Voronoi walls directly in Moi.

With some prudence!
Because there are some sharpen angles in a voronoi diagram and the input will be the best minimum acceptable of all corners!
As there are a lot of them you have all luck that your calcul fillets failed!

Maybe increase the Scale size of the all objects before make general fillet!

10 seconds for 100 objects fillets top faces : but the most difficult is to find the best accessible angle! (20 seconds :)
(I7 4 years old : not sure that the graphic card is influent to the calcul ?