Upgrading VCPKG, an internal failure appeared. I'm using v2.1.1. This is the same version working 'fine' with the older VCPKG configuration. But it looks like there may be a problem when dealing with horizontal data. In my test case, the 'minValue' = 'maxValue', causing a divide by zero condition...caught by an internal ASSERT. It actually creates a failure in qRound() as the value is set to int32::max, and the ASSERT in qCheckedFPConversionToInteger<int,double,1,1>().
qcustomplot.h, lines 21864-21865:
double valuePixelSpan = qAbs(valueAxis->coordToPixel(minValue)-valueAxis->coordToPixel(maxValue));
int dataModulo = qMax(1, qRound(intervalDataCount/(valuePixelSpan/4.0))); // approximately every 4 value pixels one data point on average