Thank you Arne. I assumed that the VST SDK 3.7 (August 2020) would have already included the fixes from the older VSTGUI 4.9 (December 2019).
Editing crect.h in your way did fix the problem.
inline CRect& CRect::makeIntegral ()
{
left = std::floor (left);
right = std::ceil (right);
top = std::floor (top);
bottom = std::ceil (bottom);
return *this;
}