vbv hanging issue; multiple slices

[Former user]

mParam->sourceWidth = 1920; 
mParam->sourceHeight = 1080;
mParam->maxSlices = 10; 
mParam->rc.vbvMaxBitrate = 512; 
mParam->rc.vbvBufferSize = 512;

preset: veryfast tune : zerolatency

x265lib version: 2.9